Develop an indicator for Solar Water Disinfection

by SODIS Foundation
Feb 5, 2013

Progress on the solar dose indicator

Setting up the radiometers for the experiments
Setting up the radiometers for the experiments

Dear supporters,

2012 has been a busy year with some significant progress on the SODIS indicator. You probably are aware that the objective of this project is to develop an indicator which can tell a user when water in PET bottles has been exposed to enough sunshine and thus is ready for consumption (for more information on this fascinating process, please visit The main challenge is to do this at a very low cost, because this device needs to go to millions of people around the world, most of whom live on less than a dollar per day.

So far, we have managed to develop several prototypes, all of which do the job fairly well. However, as long as we are working with prototypes, a lot of manual work is involved, which makes the units expensive. Thus, we need to produce on a different scale (mass production), but also to make sure that we got the design right. "Getting it right" in our case means three things:

1) The indicators need to work properly, indicating the users when they have to wait and when the water is ready for consumption.

2) The devices have to withstand very rough conditions (heat, sunshine, wind, rain, etc.).

3) They need to communicate in a very simple way with the end user when the water is ready for consumption.

In order to achieve this, we are now preparing a field test with some fairly advanced prototypes. At the moment, they are still too expensive, but before we start mass production, we need to make sure the design we are working with is the right one.

The devices we are working with are made of a radiation sensor, an electronic circuit and some kind of a display (typically LEDs). In parallel, we also work with an alternative approach: Paper stickers which change color depending on the amount of radiation received. In cooperation with the University of Cochabamba (Bolivia), we just completed a series of tests with one of these products, which shows promising results: The paper changes within 8 hours from red to yellow (see picture above). However, the product is not re-useable and the color change is slightly too slow for our purpose. Therefore, we are now looking for alternative products and for mechanisms to make the indicator re-useable.

We will keep you updated about progress on our side. If you found this report useful, feel free to share it with your friends and family and pass on the word.

With best regards from the whole project team,

Matthias Saladin

Color indicator changing from red (left) to yellow
Color indicator changing from red (left) to yellow



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Organization Information

SODIS Foundation

Location: Cochabamba - Bolivia
Website: http:/​/​
Project Leader:
Matthias Saladin
Executive Co-Director
Tiquipaya, Cochabamba Bolivia

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Combined with other sources of funding, this project raised enough money to fund the outlined activities and is no longer accepting donations.

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