Technology: SoWaDis

The water treatment technology SoWaDis (solar water disinfection) was developed at the Swiss Institute for Solar Technologies (SPF) . The WaterKiosk Foundation (WKF) has implemented this system in various countries in different social settings, usually in schools and hospitals, where the system prooved to be especially suitable. By now, the SoWaDis-system has been the preferred technology by WKF, but the more we expand our work the more we are also diversifiying in technology. Usually each location has its specific water situation for which there is a best solution.



The SoWaDis-system is characterized as follows:

The system is very easy to operate and maintain. These comparative advantages make SoWaDis a very suitable technology for developing countries.

SoWaDis is 100% solar powered and operates without electricity and supply of materials. In contrary to other available technologies the system needs no pumps, no supply of chlorine, no replacement of UV-lamps , no cleaning of filters and no electricity.

SoWaDis is producing 500 liters of clean drinking water per day. With a modular concept also higher daily outputs can be achieved. The system is cost comparative to other common water treatment technologies, especially taking into account that it requires low maintenance and operation.

SoWaDis is disinfecting the microbiologically contaminated water by heat. This is one of the safest and most effective ways of water disinfection.

Since the method is similar to boiling water, the local users understand and accept the concept from the very beginning and appreciate the safe drinking water.

Functionality of disinfection process

No additional energy, simple operation and very low maintenance are the key-factors of the SoWaDis system.

  1. The contaminated water is stored around two meters above ground. The system is gravity driven, therefore operating without a pump using electricity.
  2. The contaminated water flows into the heat-exchanger and gets preheated from around 20°C to 65°C.
  3. The preheated water flows into the solar collector.
  4. In the collector the water is heated up to 84°C. This is the process where the water is thermally disinfected.
  5. A thermostatic valve on the collectors outlet opens when 84°C are reached. When the temperature drops below it is closing again.
  6. The disinfected water flows through the heat exchanger, cooling down from 82°C to around 35°C and preheating the collectors inlet.
  7. Finally the disinfected water flows into the water storage.

System Specifications

As follows the specifications for one SoWaDis-System are listed (or to download as .pdf). The system can be arranged in parallel modules in order to gain higher outputs.

Output 600l/d (Nominal)
The average production varies according to solar irradiation. E.g. daily average in Tansanias Highland is at around 350l/d. The actual production over the year can be estimated with the local climate data.
Costs € 3000.-, ex works Switzerland, including half-day instruction-course.Please note that this price is not equal to the costs of a complete implemented project where costs for transportation, installation, monitoring, training, WASH workshops and operation coaching are ocurring. Our projects in schools have average overall costs of € 5000.-.
Weight 160kg incl. packaging
Measurements [cm] Packaged: 210 x 65 x 100Installed: 300 x 160 x 150
Lifetime 10 years plus
Max. Pressure 1bar
Maintenance Basically zero.Optional cleaning of tubes once a year is recommended. Furthermore we recommend that the clean water tank is cleaned once a month to avoid bacterial regrowth.
Field of application Microbiologically contaminated water (e.g. pond, river, lake, rainwater, contaminated piped water).
Pressure head / Feed tank 1.5 m / 0.15 barThe gravity feed tank is usually installed around 1.5 above the inlet of the drinking water tank.Depending local situation there is different ways how the water comes into the top tank. In some of our sites we have piped water that is microbiologically contaminated, so the pipe can be directly connected to the tank. In other sites we use a manual or an electrical pump.
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