Hey there,

for an easy, affordable and durable solution, try salt. :-)

Use bottles and foam trash to make islands for plants that purify water. Plants can be regularly harvested for fuel.

This concept is written up as "floating trash island" in Toolbox for Sustainable City Living

See:

http://www.lowtechmagazine.com/how-to-build-a-floating-trash-island.html

and

http://en.wikipedia.org/wiki/Spiral_Island

Some research into the Nakivubo channel reveals that a number of industries discharge into the channel and add heavy metals (zinc, lead, cadmium, and copper).  From the research article linked to here, it is evident that levels of these metals are anywhere from 5 to 100 times the levels deemed safe for drinking or cooking: http://www.academicjournals.org/ajar/pdf/pdf%202010/18%20Dec/Mbabazi%20et%20al.pdf

When selecting a water purification method, the ideal choice should address whatever impurities are found in the water, whether they are bacterial, viral, or chemical. All of the suggested UV treatment options address bacterial and viral issues, but they do not change the chemical composition of the water. Since lead, copper, cadmium, and zinc are all serious health concerns, unless the treatment does something to remove these metals, the UV-sterilized water will still be dangerous to use for drinking or cooking.

Heavy metals are very difficult to remove using simple, small-scale, and low-cost water treatment methods. As the article points out, the wetlands are able to remove a large amount of the metals, so solutions like the vetiver vegetation mats are quite interesting, but this is more of a community-scale solution than a household-scale one. In the end, you may want to consider multiple solutions like perhaps using filtered channel water for things like washing clothes, but finding an alternate source of water for drinking and cooking that you can be sure won’t be contaminated with metals. One of those alternate sources might be to employ rainwater capture systems which are gaining popularity in Uganda.

http://www.wateraid.org/documents/plugin_documents/rainwater_harvesting.pdf

http://akvo.org/wiki/index.php/Rainwater_harvesting

http://ugandanwaterproject.com/

The ability of Vetiver Grass to act as a primary purifier of waste water:
an answer to low cost sanitation and fresh water pollution.
By Mark Aaron Gerrard
202302385
10/03/08

http://api.ning.com/files/KDIZ-vGToONTzPwNKlk-RmMUFqXYBHLB7iSOrQOl3eUDGfMOMwxRU0VXkeFCb1boRBGn4rgSu7hnxDn6N4walRh1EYNB2EvC/HydroponicVetiverRafts_phytoremediation.pdf

Hi everyone,

• If you want to raise money, definitely we need a website with more information to establish credibility (partners, photographs, more information on the location of the slum, precise google map,...) Actually you can crowdsource this: take photos and info, then post a challenge here on SWB. People who are web-savvy will be more than willing to help.
• For cleaning water, a lot of people have already mentioned solar disinfection (SODIS http://www.sodis.ch/index_EN ). The method is explained clearly on SODIS site. This is a CNN video of their application in slum in Kenya: http://edition.cnn.com/video/?/video/world/2009/09/01/mckenzie.sun.water.cnn
• More (expensive) product, beside already mentioned http://www.solvatten.se is : Life Straw http://www.vestergaard-frandsen.com/lifestraw . If you create a website maybe you'll get a Life Straw product donated to your initiative.

If you want to brainstorm further with me, feel free to email me at toanvphan@gmail.com .

Best,

Toan

According to WHO 2004 It is estimated that 88% of diarrheal disease is caused by unsafe water supply, and inadequate sanitation and hygiene (WHO, 2004c). The water which is drawn up from the ground and travels through poverty stricken areas is loaded with about every type of pollution there is. With little room to put trash and other waste, children even play in and around the area of the channel. There is already an issue with trash throughout the area. I am understanding that it is not the entire city that has the issue, just the poor that cannot afford the fresh water supply, even to use for washing. This is an issue which unfortunately everyone in this city needs to deal with, including the Ugandan government. It is also unfortunate that governments around the world forsake their people every day, and can rarely be counted on to solve any real issues. Even industrial water treatment centers of small scale do not handle things like plastic bags, ect. so spending money on them would not solve the issue. Only through communication with unwilling government and the people can this problem be solved. Your first issue is the trash, as it needs to be removed from the water before you can even think about cleaning it.

I think that possibly the best way to solve at least some of the huge, and serious issue is through education. With this I mean that people of the entire city need to change their habits when it comes to the use of their own water supply. I do agree with all of these solutions presented, and it is definitely true that you need to start at the start. With this there is a good book to read that has many good informational points regarding this issue, but on the smaller scale of a school in mind. I did also find it on the surface web thankfully for you to take a look at. There is a great checklist to follow on chapter 5. Thank you for the additional information since I cannot personally be at the site to assess it. Just glancing through it I can probably assess that most of the answers to the check list mentioned above are no.

Several issues need to be overcome first, and all, one at a time. First there needs to be an area out of town dedicated to putting the trash that is in the channel, this issue brings forth more issues as to where the “legal” dumping sight for the entire city will be. Next is how exactly to get the trash there. I am sure that the government claims most of the land and will have a problem with using any area you mention solely for trash.

There is however a solution. Perhaps if the government would be inclined for their own benefit to build an electric generation plant that ran on trash. I use this solution because there are many across America, and not only are they self sustaining, but profitable for the government, and private business. If there were a way to convince them to construct one to supply their own cities with electricity you would then have a place to bring the trash. Coupled with this you would only need mention the slum areas for the fact that there is a rich supply for energy there as the plant is built and not before. They might even be inclined to remove the trash and transport it for the generation of electricity. Of course there is no way to know how this government would react to such a suggestion.

Another thing that might complicate this is to have a private company come in and build the plant. I would strongly suggest against this idea since in the end the company would only want more money from your government to build such a plant. This would have to be done by the government; otherwise the government would put a stop to it. In the end the plant would have to be large enough to literally suck the trash from every resource it can find to operate and sustain, but not so much that it fails to sustain in the future.

The next issue is educating people around the Nakivubo channel of the serious risks to their own health. Especially if the government did not want to build a power generation plant; the people around the channel need to get involved in it’s cleanup, which leads back to where to put it, which again involves the government. Currently there are many spots where people simply dump trash, and it inevitably ends up into the channel. Though the government does not currently care about this, where to put the trash needs to be addressed first if they are unwilling to build a power plant.

About sustainability; it is a seriously complex issue since human’s needs typically are greater than waste area. It is obviously out of the means of the poor to purchase. Anything less than large scale water treatment plant; and there are water treatment plants that are about thirty thousand U.S.D. for one that will not be large enough to deal with this issue. So this would definitely not solve the issue. The cost issue is also beyond the simple purchase of equipment, but the money for chemicals needed to clean the water on a daily, monthly and yearly basis, and the transport of these chemicals would make the system even further out of the question. We would not only be talking about cleaning the water but making the Ph something that people could use even for cleaning much less drinking, which is only something for the future. This is why it may be best to consider a change in thinking of the people involved for their own betterment.

I also think you have taken the correct approach in thinking of ways to deal with the issue without spending peoples money to do it. Though it will take time, and more effort than many of them would be aware. They now cannot possibly escape the physical labor involved to clean their own water. This ends up to be an aboriginal view of the issue of how people have been dealing with clean water issues for thousands of years. With this I mean that it will take everyone in this culture to bring this very difficult and serious problem to a halt, and maintain the clean water supply. You will also not get to a solution without government diplomacy. This is very unfortunate, and from here involving the government makes things more of a complex challenge.

In total the solution to this problem is found in finding a place, involving the government and the people to transport the trash. This means all of the people, especially those in the slums to actually take the trash which is currently in the channel out of it. Then making use of the trash. From here we can definitely find a way to clean the water. This is just the first tiny step in a process to change the environment for sustainability. I am sorry it has to involve an unwilling government, and in the end their greed will most likely make this issue something that has to be resolved by the people themselves. I would advise however to at least approach the government with this first. Since an electric generation plant is self sustaining perhaps in the beginning the poor could help in transport of the trash, then fine cleaning of the channel can be obtained.

It might be to note in the future that the issue with the slums of the city were the spur to generate power. If the generation plant is spurred from the issue in the slums and eventually creates funds for the government though unlikely, perhaps they might consider funding clean water solutions for the future. You might also get a chance to make this work for sure with a change of Presidents in Uganda. With the throwing around of promises of new jobs this new event is a wonderful coincidence, and with the thought of all of this comes new services that can be provided with new promised jobs. Something to move on now, and not wait.

“Peace is a path we must walk with intent, it is not a destination. Every step must be taken by every person to walk this path no matter how difficult it is to walk.”

 – Thomas Mind

I hope this is the beginning to a larger solution.

Steven Aulisio

Pilot- 3124384
  Electrical- 11763-B Massachusetts

References;

http://www.unicef.org/wash/schools/files/rch_who_standards_2010.pdf

WHO/UNICEF (Editor); Simms, J.; Chartier, Y.. Water Sanitation and Hygiene Standards for Schools in Low-Cost Settings.

Albany, NY, USA: World Health Organization, 2009. p iii.

http://site.ebrary.com/lib/ashford/Doc?id=10367459&ppg=3

Copyright © 2009. World Health Organization. All rights reserved.

As others have suggested, using sunlight to purify water is a possible acute solution. There is a product called Solvatten that utilizes heat an UV from the sun to sterilize water.

Disclosure: I am friends with people directly associated with Solvatten, but i have no personal financial interests in the product.

From the web page, at http://www.solvatten.se/ :

"Solvatten makes unsafe water drinkable by using solar energy. Put Solvatten in a sunny place, give it 2-6 hours and the water will be drinkable! This can be done twice, sometimes three times a day, producing  20- 30 liters.

It is common knowledge that boiling can make water safe to drink. But it is not as widely known that UV light also kills micro-organisms. Solvatten is a specially designed container that uses heat, UV and a built-in filter to clean contaminated water. The patented Swedish invention Solvatten inactivates micro-organisms that cause diarrhoea and disease, producing water which meets the WHO’s Guidelines for Safe Water (<1 E-coli/100ml water).

Solvatten can treat water containing bacteria, viruses and parasites. Solvatten don’t use the aid of any chemicals or any energy-source except the sun. Treated with care you can expect approximately 5 years of trouble-free use.

Solvatten has an indicator that shows the user that the water treatment process is complete."

Potential financing

An innovative suggestion for financing is to use Solvatten to compensate for carbon dioxide emissions. An individual or company could compensate for their CO2 emissions by donating a number of Solvatten water purifiers.

Again, from the solvatten webpage:

"The process of boiling to treat and heat water consumes large quantities of fuel, often firewood collected locally. Since the trees are not replanted, the resulting deforestation contributes to climate change.

SOLVATTEN® is a groundbreaking technology that uses solar energy to treat contaminated water for drinking, as well as producing warm water for cooking and hygiene. The SOLVATTEN® technology has been highlighted by WWF Sweden as a climate-solving innovation, on the grounds that it can give millions of people in developing countries access to safe and warm water, while at the same time avoiding deforestation. The potential reduction in carbon emissions by 2020 has been estimated to be 26 million tons a year.

Each SOLVATTEN® unit holds ten litres, and can treat water up to three times a day. This corresponds to a saving of up to two tonnes of carbon emission per household per year, depending on how much water is used and how it was treated previously. Two tonnes corresponds roughly to the emissions from driving an average car for a whole year.

Since use of SOLVATTEN® technology reduces deforestation and the resulting carbon emissions, the purchase, distribution and use of the units can be funded through “carbon finance”."

May be a good idea to get an inexpensive water analysis to see what is in the water, including other chemicals and metals. This would help you decide what system to use. Can you obtain a water test locally? If not then you should be able to find a water chemist to help from Scientists without Borders by putting in an assistance request for water testing. The next crucial question is what is the intended use of this water channel? Does domestic use include drinking water for the 15000 people or only washing? Was this intended to serve as an open sewage channel? The answer to these questions makes a big difference as to choice of strategy. I am addressing the problem as if this is the drinking water source for this community rather than an open sewer. If this is intended to serve as the sewer system then that is going to require a completely different solution.

Ultimately you want to prevent or recycle the untreated waste from being dumped in the water, but this could take a while to implement and is more expensive so you may want to first start with household filtration. For this many people you are going to need a financing strategy. If direct subsidy from a local government is not available, I would try direct contribution from a local NGO. Otherwise you will have to try to get the community to pay for filtration somehow either by buying houshold filters from you or contributing to a community filtration project. You may also use a combination of sources. If you are very resourceful you may be able to produce your own filters at a very low cost and sell or barter them to local people affordably. Once you decide on what type of project is suitable and have a plan, I can try to help you find funding. ADDENDUM: I read in your discussion that this channel was originally a World Bank project. I would contact the World Bank and show them what is happening with the project. With any luck this can lead to some remedial action at the World Bank level.

Depending on what is in the water, at the individual level you can mass produce household ceramic filtration systems (or try to obtain them at low cost through from Potters for Peace). This web site provides step by step instructions on how to go into production: http://s189535770.onlinehome.us/pottersforpeace/?page_id=125 . The same organization should be able to provide other guidance for setting up and for obtaining financial assistance for materials. Perhaps you already have a pottery shop in your community or are handy enough to construct your own shop and equipment. Remember that the silver is not essential, although with the silver the system is more effective. The filtration rate is about 2L per hour or almost 50L per day if used round the clock. This rate is considerably faster than SODIS systems which means you would need far fewer of these per person. You could try to set this up as a business where you sell the pots for a small sum to help pay for the materials and equipment. If the idea catches on you could continue ad infinitum since the pots do need to replaced from time to time. A simple factory can make about 1000 pots per month. In less than two years, you could be supplying the entire community.

The next step while providing individual filtration should be a community water filtration facility. You will have better health results if you centralize (could be many smaller facilities rather than one for all 15000 people) and supervise the water treatment. There are two processes I particularly like that have been proposed for smaller communities at minimal cost. The first is a tubular ceramic filtration in combination with an anodic oxidation process powered by one solar panel. The membranes are cleaned by simple washing and no chemicals are needed. One unit produces about 500L per day. These are mobile devices that can be installed all over the place or moved from one area to another. For more information on this system contact Professor Groendijk at leo.groendijk@wur.nl

The other type of system is Iron Oxide/Sand filtration which can reduce the typical water treatment steps of flocculation, sedimentation, rapid sand filtration, activated carbon filtration, and disinfection into two simple steps. For more information on setting up this system in your community please contact Professor Noubactep at cnoubac@gwdg.de

These professors have invented these systems so I prefer that you work with them for more details. I am a policy specialist, not a water engineer. You want to move towards a community system as quickly as possible, but since this could take a while you would first provide household systems on a gradually diminishing basis.

The SODIS system called Solvatten mentioned elsewhere is very good too if you can obtain enough of them and make the people use them. You could also invent a way of fabricating your own 'Solvatten' using local/waste materials and waste as has also been suggested (plastic bottles). Be aware that the heated plastic may release other chemicals into the water and the water should be low-turbidity (not cloudy). This often requires a pre-treatment which could be done through flocculation using a local material such as some vegetative matter. You also need many bottles for 15000 people and the process can take a long time, from 6 hours to 2 days on couldy days. In the end, SODIS may not be as easy or effective as ceramic filtration. A community level SODIS treatment plant is an interesting concept but I have not seen any designs yet. You would need very large holding tanks and a pumping system for this to work and possibly pre-treatment for cloudiness. You could use discarded DC motors to power pumps.

Wearing shoes can also be a powerful defense against disease. You may be able to obtain used shoe donations from a local NGO.

Good luck and let me know how things are going.

Please consider that you have lots of options with the Solar. Some of which you already have noted from previous solution suggestions:

1) You can utilize solar energy in a parabolic reflector or with mirrors to boil water or greatly speed up its evaporation for distillation purposes, or generally intensify the solar radiation. If this is not a large volume process, it could provide drinking water.

2) Storing boiled or distilled water in clear plastic bottles in the sun would give an additional treatment of the water to kill micro-organisms.

3) Even without a distillation apparatus, immediately moving to SODIS to suntreat water in clear bottles would greatly decrease the organism load in the water now being used without any treatment at all.

4) Making sure everyone in the community understands the basis for the illnesses is critical to making it work. Communities can be very resourceful. Community education developed by the local children for example is a good way to spread the word. Children making up their own songs in school for controlling mosquito larvae in central and south america. That has been very powerful in reducing malaria in local communities. The education never worked though, until it was placed with respect in the communities hands and responsibility.

Are you looking to reuse this water for drinking and/or for household only?

Here are the options that I know of:

1. Point of Use (pair with safe storage)
   • Boiling
   • Slow Sand Filtration (for clusters of households, but generally more effective on community scale)
   • Clay Ceramic Filtration
   • UV Filtration – Sunlight (SODIS)
   • UV Filtration – Lamp (for household or clusters of households/dormitory setting)
   • Coagulation Flocculation – Morina/Plant Fibers (Filtration and Aeration technology)
   • Water Treatment Packets
   • Chlorination
   • Bleach (NGEGEA)
   • 3 buckets (Tanzania)
2. Community Scale
   • Sedimentation and Settling
   • Membrane Filtration (usually used in developed nations)
   • Granular Media Filtration
   • Slow Sand Filtration
   • Coagulation Flocculation – Conventional (Filtration and Aeration technology)
   • Coagulation Flocculation – Morina/Plant Fibers (Filtration and Aeration technology)
   • Adsorption (charcoal or carbon mixed into media filtration)
   • Chlorination
   • Riverbank filtration

It seems like this should be, at least, a three step process and possible steps have been suggested: 1) Eliminate the waste source(s), if the main problem is human waste, by providing toilets (perhaps composting toilets) and education. 2) Clean the waterway and (re-)establish a healthy ecosystem. 3) Purify the water for drinking.

Using Effective Microorganisms to Clean the Waterway

Effective microorganisms aka beneficial microbes have been increasing in use, since the 80s, for bioremediation of bodies of water and soil that have been polluted with human waste, petroleum and other chemicals. It has been used effectively in many areas including the Seto Inland Sea, Japan; Ilusiones Lake, Mexico and Bogota River, Colombia.

The implementation this treatment is exceedingly simple: inoculate locally available mud with the microbes, form the mud into balls, then, after two weeks of fermentation, throw the mudballs into the water that needs cleaning. These very dense, heavy mudballs sit on the bottom of the body of water slowly releasing good microbes over days or weeks. This can be done by all ages and is fun and educational for the community.

NOTE: I have been keeping track of progress on the item.  See below.

Currently, a makeshift prototype is built and is in testing.  The prototype is being modified constantly to address issues.  It's quite trial-and-error.  See the Mar 01 update.

Original Initial Post:

Disclaimer: I am going to workup and test a quick prototype idea of this, but I will submit the idea itself now.  My idea will not clean the waterway, my idea focuses only on the anthropic aspect of the problem, the problem of the people drinking water likely full of both infectious and toxic agents.  Since one cannot place pictures on this website without a website of one's own, I will try to describe it.

If the water were to be evaporated and condensed before it is drunk, many of non-airborne parasites would be left behind, as well as heavy metal toxins and many (though not all) water soluble organic compounds.

A large clear plastic garbage bag could be used to make a makeshift greenhouse, with a bottom surface area of about 1 m^2 (to make mathematical estimates easy).  Inside the bag is a frame, likely of wire or PVC or something even cheaper, which holds the bag upright at the edges.  This frame props up the sides, so that the bag sags in the center.  In this center, a cup hangs.  On the bottom of the bag is a surface painted or fixed with some melanin, perhaps affixed to a sheet of plastic, metal, or paper. In the bottom, with the melanin sheet, is where dirty water is placed.

The melanin base will increase the absorbance of UV, visible, and infrared light, dissipating this as heat into the water (via 'ultrafast internal conversion, see wikipedia article if interested).  This should heat the water nicely.  We do not need to boil the water, merely to heat it so as to increase its vapor pressure.  On the large sagging upper portion of the bag, which is in contact with the air and therefore cooler than inside the system, water will condense.  Because this portion of the bag sags, water will drip downward into the cup, from which it can be drunk.

The reason for using melanin is melanin's wide spectrum of absorbance in the UV and infrared, and it's high absorbance throughout that range.  From personal experience, it is so efficiently absorptive in the visible spectrum that purified melanin, or a high concentration of Aspergillus niger spores, are actually hard to see - the surface texture being so pitch black that it almost could not be seen, because it absorbed visible light so effectively.  Also, this should not increase the cost because Aspergillus niger spores are incredibly easy to grow and obtain, often to a culturers dismay ^.^  I will see if controls, such as simple black paint or black construction paper, also work.

I did some quick theoretical 'proof of concept' calculations for this idea (hence the 1 m^2 earlier).

I found on the internet a reference stating that the average solar radiation on an area near the equator is 400+ w/m^2 (see wikipedia article on 'Insolation').  This is at the top of the atmosphere, so the amount is lower, thus I will use a fudge factor and assume half that (which should give me a margin of error).

Assumptions: 200 w/m^2 = 200j/(s*m^2) as an approximation, and assuming perfect absorption (absurd, I know, but call it part of the fudge factor).  2270 j/g as the heat of vaporization of water (I believe this is still valid at temps lower that boiling since we are still relying on a phase change liquid --> gas).  Assume system 1 m^2.

200 j/s/m^2 * 1m^2 * 1/2270j/g = 0.088g/s

0.088g/s * 3600s/hr = 317 g/hr.

So just under a liter of water in approximately 3 hours, at theoretical maximum.

Now, the system is cheap, makeshift, and inefficient, and will likely have some condensing on the sides, and some cooling from being placed on the ground, so I shall add another fudge factor, and estimate another 50% loss of energy (the approximate surface area of the sides). As such, lets say it takes ~6 hours to produce a liter of water.  One thing I do not know is whether the 400 w/m^2 is averaged over the whole day, or just when illuminated, so lets assume the lower value to remain safe, thus we can assume about 12 hours of light.  So the system will produce around 2liters in a 12 hour period, an amount of drinking water for one person per day.  They won't be able to bathe with it, but it is a start.

Benefits, as I see them, to this system (I have this post community editable, feel free to add more, or to comment):

1. If I can make it cheaply enough, it could provide a temporary, light (PVC + 1 plastic bag + 1 sheet plastic or paper + 1 cup or bucket), easily distributable, easily reparable mechanism, which if cared for can last a long time, to mitigate the human problems associated with the poor water quality in the area.

2. Gets rid of non-airborne microbial contaminants and parasites, heavy metals, water soluble organics (and generally high MW organics), and such.

3. Large numbers could be kept at a central location, such as the roof of a local hospital, so that water can be distributed to those that need it and less people need to be trained in their use (see Problems section)

4. because of it's shape, this 1m^2 sagging plastic bag can catch rainwater, so when the sun isn't shining, it is still potentially producing.  I should look, at some point, at the local weather for the area in question to see if this is important.  I'de be a little worried about bird feces...

Problems that I can see at this moment (Again, I will leave this community editable, so feel free to edit and add more, or to comment.  Make sure to give yourself credit when you do, so that it doesn't look like I am plagiarizing.):

1. It still might be too expensive for your purposes, I will have to see.  15,000 units, even at 5 USD/unit, still comes out to be a pretty penny.  It might be necessary to make fewer, or fewer larger units for families or even for communities to simply lower but not entirely remove the need for fresh water.

2. If used incorrectly, it could cause problems: for example, if one does not change the water in the bottom, slightly volatile organics can concentrate and increase in concentration in the drinking cup water over time.  Same problem if they ever let it almost completely dry up: then one could actually get a higher dose because less volatile things will be volatilizing and condensing into the water.

3. Similarly, any toxin more volatile than water has the potential to be concentrated in the drinking cup rather than removed.

4. Again, if they don't change the water: mosquitoes = malaria, among other stangnant water problems, and we don't need any more of that.

5. To mitigate the other problems, many people might need to be trained in how to properly use them in a way that will not cause more problems than they solve.  This takes someone willing to do so, time, and possibly a bit of money to pay them for it.

6. It is likely to be nowhere near as efficient as my calculations lead me to believe, regardless of fudge factors, so may not work (hence the proof of concept experiment I shall do).  If it doesn't, I will remove this thread with apologies.

Need to do:

1. I need to actually build and test one.  Because I live in a cold climate, I will use a heat lamp at a given distance to simulate the sun.

2. They would need to be tested somewhere on site before anyone were to try to make a bunch and distribute them, including testing the water under various conditions to ensure that it is in fact safe water.  This should hedge out any potential problems so one can figure out what not to do with them (again, I refer to stagnant water and excessive drying).

3. They might be cheaper, or possible to make cheaper, depending on where one gets the materials.  I will need to find out how cheaply I can make it, and compare all materials and sources.  The price in the storefront is most likely a large markup from what it could be.

PROGRESS REPORT:

I have now most of what I need to build the object now.  Design will be based on what I could get ahold of cheaply, but it turns out that the items may be CHEAPER than I thought, AND may be cheaper yet if made in slightly different ways.  For example, I am using PVC for the frame, but sticks lashed together with some old cloth at the joints might very well work perfectly, completely getting rid of the cost therein.  At this point, the only reason I am using PVC and plastic garden-plant stakes is because, as mentioned, I live in a cold climate, so all the good sticks are burried in snow right now (If I felt like being more resourceful, I could probably still find some quite easily ^.^).  That said, the entire thing could, concievably (and depending on what works best) be made using little more than the cost of a garbage bag and something black to soak of light, and some old cloth or string.

I still need to actually put it together and see if it works.  But here's what I've got:

Frame: PCV and gardening stakes.  Cost for both PVC, PVC joints, and the plastic/metal stakes, will be about 8-10$ for my prototype.  This could be much cheaper, as I mentioned just above, because one could use just old cloth (to pad the corners) and sticks or bamboo or similar.

Plastic: Plastic garbage bags.  The largest I could find off-the-shelf was just over a meter by just under a meter, though with the needed height, lets assume that with that, the final product will be about ~0.8 meters by ~0.8 meters, to account for edges.  I will do all calculations accordingly, and this is close enough. The bags cost 15$ for a box of 45, so ~0.33$ each.

Pigments: I want to try several ways to get black stuff on the bottom of the bag.  I bought 1 can of black oil-based paint (so that it resists the effects of having water in it for long periods of time).  I have a bunch of black construction paper.  And for actual melanin, I just, about 20 minutes ago, put some Exophiala werneckii in to grow.  E. werneckii will take a little longer to actually grow and make enough melanin to be relatively black or to have enough to be worth extracting (which is cheap, involving litle more than hot HCL), but it is a yeast so can be more easily grown in huge quantities, and won't contaminate our whole lab and get into all of our cultures the way Aspergillus niger does whenever I grow and isolate large quantities.

Light Source: I bought a variable lamp, with 3 settings: 200W, 500W, and (200+500)=700W power.  My calculations above assume a solar exposure of about 200W/m^2.  For further adjustment, I can vary the distance at which it sits above the system.  That way I can keep it far enough away from the actual setup to not be a danger to it, since at even 200W, it's going to get VERY hot.  I am depating whether it would be a good idea to remove the UV shield on he front to better simulate sunlight, or to just leave it on since the whole setup is pretty makeshift anyway, and it shouldn't change very much anyway ^.^  But I worry that this, what looks to be plexiglass, 'shield' would also block some IR, which would be bad...  But I am setting the whole thing up in our kitchen and I don't want to damage our retinas ^.^  Maybe I will only turn it on at night and have everyone know not to look at it, or go near it, until I unplug it in the morning.  And I can cover it with a blanket.

NEW PROGRESS REPORT (Feb 8):

I built the apparatus just now.  Turns out it was easy, and turned out nicely without any of the problems I anticipated like bags ripping and such.  With a hacksaw and measuring tape, I built it in literally about 1 hour, and it looks workable.  That one hour INCLUDES time to repeatedly realize my things were too large, disassemble, cut pieces, reassemble, ect.  All that would be unnecessary if making it to a standard size, thus they would be easy to mass-produce if necessary.

The final dimensions of the specific one I built are 10" x 23" x 27", or 0.254m x 0.584m x 0.686m, thus it has a surface area of 0.4m^2.  I am sure that, if we were to want larger ones, we could find some source of larger clear plastic bags, but again, I am just using what I can buy in town relatively cheaply.

My objective is something super cheap, so I can now reitterate the costs I would anticipate with mass-producing these:

3 clear garbage bag: I misremembered the number of garbage bags in the pack that I bought for 15$.  It was in fact 70, so each one costs 0.21$.  The reason I say 2 is because A. I think there might be a way to make the thing more efficient if I use 2, which I will try, and B. we have to take into account the possibility of the bag ripping and needing to be replaced.  That said, 3 bags is about 0.63$.  However, this might go up in price if better bags are used, because my current ones are just clear, pull-closed yard-bags, but it might be better to use bags of a higher mil (mine is 1 mil, which equals 1/1000 inch.  While at the store, I saw plastic (though not plastic bags of sufficient size, hence why I didn't get them) of up to 6 mil in huge rolls, or up to 3 mil in smaller rolls or larger.  The problem is that these rolls of plastic were always particularly expensive, and would need to be cut and require tape to hold together, something we probably don't want to rely upon if making something for long-term use in africa with water.  I should also mention that it might go down in price if we can get supplies directly from the manufacturer, thus subverting the markup from the store.  So better materials = Increase Price, but direct purchase in bulk = Decrease Price, so really it's hard for me to say where the price of the plastic bags will actually end up.  If the exact ones I used were to become the norm, though they are a little smaller than I had hoped, they would cost 0.62$ each, and the cost for 15000 would be ~10k$ just for the bags.

I don't know how much the black surface will cost to produce.  I need to go to the art store to see about an oil non-pigmented base, or just cheap black oil paint, in which to mix the melanin for my quick melanin trial.  Construction paper is also very cheap, and if black paper works, SUCCESS!  We could even have a semi-fundraiser where we ask for people to secretly print pages of black paper and donate them.  Also, I could perhaps give a try to Carbon Black residue, which has chemical properties sort-of like melanin in that it is a massive super-arromatic molecular structure, and which for some reason I've been collecting because I think it looks cool whenever they empty the copier's toner cartriges.  It would be funny to see that stuff actually come to use... It would help me further justify my hoarding addiction.  Also, if that DID work, it would be an excellent way to have a super-cheap black pigment for the surface, because the stuff is literally a byproduct of almost every large copier with a large black toner cartridge.

Now, if the frame were made of sticks lashed together and padded with old discarded cloth, that leaves only other modifications to increase the cost.  For example, kpmitton suggested, in their entry titled Using Solar to the maximum, reflectors.  Such reflectors could be aluminum foil on cardboard, or old, shined-up roofing metal, or the similar.

Since it is possible that the bottom of the bag will encounter some wear-and-tear, it might be good to put some sort of cheap pan on the bottom in which to put the black surface for absorption, so water can just be put in the pan.  I don't know how much that would cost, but it could actually be made of scrap metal, bent into pan-like shape, or I wonder, even large leaves if necessary?  Anyway, this is another thing that might make the whole thing better, since you no longer have the bag on the ground, which would help the bag last longer.

One thing to note: I said it would be light-weight.  My prototype made of 80 schedule PVC and my 1 mil bag, along with some random garden stakes, weighs 12N = 1.22kg = 2.7lb, and I can pick it up with my pinkey finger.  I just took it apart, and it takes about 2 minutes to take apart if not hurrying, and 4 minutes to set up, again if not in a hurry.

March 01 Update:

I found a guy who has a nice demo of this sort of thing on youtube.

http://www.youtube.com/watch?v=4sqRvUzqDCE

The concept is really easy.  Any person with a little know-how and inginuity could start looking around their area for stuff that would work.  In he video, he also makes a nice demonstration of what I was pointing out earlier, how some toxins might be a problem, because they might even concentrate in the final water.

One thing that has been a large downfall of the system is that so much water condenses on the sides.

Also, the trouble with scaling the idea up to a half-meter by a half-meter has been that the drips don't even make it to the little cup in the center.  The reason for this is mostly because my system was not sloped enough.  If a droplet anywhere near the edges or middle nucleates and grows large enough by engulfing those around it, and begins flowing down, it grows so quickly large enough to drop right off and right back into the evaporation spot.  To slope it more, however, requires that I decrease the size so that the clear plastic bag can sag more.

I have a second solution, however, that requires the same scale-down, BUT will actually collect significantly more water: Instead of trying to collect water in the tiny center of the apparatus, while half condenses on the sides and lots of energy is lost, and the radius over which water collects and actually makes it to the container is small, I will have a pan in the center and collect water on the sides, and have the plastic bag 'tented' in the middle so it all runs off to the sides, to be collected down below.  The 'pan' is a series of sticks with a black plastic bag around it (I am just using an autoclave bin we had conveniently handy in the lab), so that it absorbs light nicely, and is waterproof so can hold the water just fine.  This is propped on the setup, such that the water condenses on the top and drips off to the sides.

One major benefit of this is, even if some drops farthest away from the colecting area do not, in fact, make it to the collecting area (falling off prematurely), the area over which the drops ARE collected is much larger.  When the bowl is in the center, the area is just the radius around the bowl, a mere circle.  Lets say 10cm for random arbotrary head math: then the actual succesful collection area is 10cm^2*Pi = 314 cm^2.  If, however, the edge of the apparatus is used, and assuming a circular system (it's not, but for the purposes of my demonstration that's good enough of an estimate), of a system 50cm in diameter, then the collection area is 25cm^2*pi - 15cm^2*pi = 1256 cm^2.  A bit of a drastic difference.  Not to mention use of the sides, rather than the sides being but a bane, thus increasing output further.

Anyway, I need to go cook dinner, good night all!

I do not know if this is practical on the large-scale but some communities have been using the sun's ultra-violet radiation as a cost-efficient way to sterilise water. A report on one such program can be found here. Coarse filtering would be required beforehand.

Boreholes will at least provide a safe source of (ground)water for households, although along the distance you mention, multiple would be required.

There are mutliple organizations that fund this type of project; inlcuding this one, which I note is already working in Uganda: http://www.startwithwater.org/search.aspx

For the river itself, what is the source of the pollution? Is it mainly local (e.g. sewage from residents of the area) or are there other sources (industrial / chemical?) If loca, education could make an enormous impact; which might include self-composting latrines, as the other user mentioned. Education would also be needed if boreholes were put into place; so ensure their use.

Slow/bio sand filters are one of the cheapest means of purifying water.

See:

http://www.biosandfilter.org/biosandfilter/index.php/item/229

Start with latrines. Composting latrines would be good. See:

http://www.ecosanres.org/toilets_that_make_compost.htm