Develop an indicator for Solar Water Disinfection

by SODIS Foundation
This SODIS indicator goes from red to yellow in 6h
This SODIS indicator goes from red to yellow in 6h

Dear supporters,

This is the final report on our project to develop an indicator for Solar Water Disinfection (SODIS). The goal of this project was to develp and test a low-cost device which can tell users of the SODIS method when the PET bottles which are used for this process have been exposed to sufficient amounts of sunlight. During the course of the project, we tried several approaches to solve this problem:

- Materials-based approach: Some materials change colour according to the amount of sunlight they receive. This fact can be use to produce a SODIS indicator, and in fact we identified a producer of an adequate product and carried out field tests with it. It works well in the field, but the drawbacks are the fact that the indicators can only be used once and that the price per unit is fairly high - 0.40$ may sound like a small amount, but each user family will need at least 10 to start with, and that's already 4$ - and then they will need more... However, the product works and the SODIS Foundation will continue to use it where it sees a need and a benefit in doing so - for example in situations where there is not enough time to train people thoroughly, like it is the case in some emergency siutations we are attending at the moment in Bolivia.

- Electronic approach. We have supported and collaborated with several groups (both research and private sector) around the world who are working on the development of an electronic device which measures the amount of sunshine received and tells a user when the water in the bottles is ready for drinking. Two of these groups went ahead to set up formal organizations ( and, who we mentioned earlier) and are currently undergoing field tests of advanced versions of their prototypes. The advantage of these devices, as compared to a single-use device, is that they can be used for a long time (several years), which makes for an ideal training and teaching device. The drawback is the prize - but this will come down as the numbers of units produced increase. We will keep in contact with these organizations and actually may field-tests some of their products later this year. 

Thus, we think that we have reached a stage where we can close this project. Over the past years, we have developed and tested several prototypes, supported research around the world and helped to establish two companies. We hope that this initiative will continue evolving and wish all the people and organizations involved all the best - for that in the near future, a SODIS indicator will be available for everyone who needs one - potentially, that would be at least 870 million people who currently do not have access to safe drinking water!

If you have questions or comments about our project, please do not hesitate to contact us (

At this point, we also want to thank all of the people who supported this project. Without these inputs, we could not have done all of this, and we also want to extend the thanks of all the people who directly benefited from this project.

Best regareds from the whole project team,

Matthias Saladin

The quest for the development of a low-cost indicator for solar radiation continues. In this report, we would like to comment on some exciting developments we observed in the last few weeks:

- One organization we mentioned several times already, Helioz GmbH of Austria, are in the process of producing a first series of their electronic SODIS indicator. The SODIS Foundation is one of the organizations who will be able to try the indicator under real-life conditions.

- A group of investigators and designers from Italy are working on a novel approach for the SODIS indicator. The idea is to have a material which changes color after being exposed to sunlight, and which can be used several times. This would significantly lower costs of producing such indicators and transporting them to remote areas.

As you can see, several groups and institutions around the world are working on the same objective, independently from our work but often in a collaborative manner. We will stay in contact with these groups and discuss ways on how to implement the different approaches in the field. A key question we need to address is how the indicators are used: either by the users directly (which means we need a lot of indicators, but probably will create more trust and a richer experience for users) or by trainers of end users, who will use there devices as a teaching tool for the surrounding families (which means we need fewer devices, but people will not be able to obtain first-hand experience).

We will keep you informed about these and other developments in the coming weeks.

Best regards from the whole team,

Matthias Saladin

PS: In order to avoid misunderstandings, we would like to make it clear that the activities of the groups mentioned in this report were not financially supported by the SODIS Foundation. The donations received for this project through Global Giving so far have been used for field testing in Bolivia and for coordination activities of the SODIS Foundation.

Dear supporters,

We wanted to let you know about the exciting latest developments at our project. As you may know, we want to develop a device which tells users of the SODIS method (Solar Water Disinfection) when a bottle has been exposed to sufficient amounts of sunshine and the water is safe for drinking. We have been working with several companies and research groups around the world, and so far we have focused on electronic devices. However, we are now also using a second approach, which is based on colour-changing materials. These can be delivered in the form of stickers to the users, taking up very little space and for a fraction of the cost of an electronic device.

In May and June, we have been in contact with a group of scientist at Queens University in Belfast (Northern Ireland), and they have advanced significantly in the develpment of a prototype. Basically, they exposed different colour-changing materials to strong sunlight and measured how quickly colour changes. The results look like a bunch of coloured dots, but based on these results they can develop an advanced prototype, which we then will test in the field. Ideally, we want to have a material which is re-usable for many times, but this is a major technological challenge (the materials need to "recover" overnithg). Thus, for the moment we will work with disposable materials, but also keep derveloping the re-usable ones - they will be more cost-effective, save limited resources and produce less waste.

Please let us know if this report has been interesting and useful for you. If so, please share this message with someone who might be interested in this project and in supporting our cause of improving drinking water quality of marginalized people in Latin America. Obviously, we are still several months away from a finished product which may benefit millions of people. In the meantime, if you want to support a project with immediate impact on improving drinking water quality, have a look at our micro-project for 18 day care centers in Cochabamba (see link below).

Best regards from the whole project team,

Matthias Saladin

PS: Just to avoid misinterpretations, we would like to clarify the the work of Queens University is directly funded by institutional donors, not by the SODIS Foundation. Our support focused on establishing links between different research groups and to identify an ideal place for field testing. The funds we receive through Global Giving are used for our own tests and for coordination activities.


Dear supporters,

Our project to develop a low-cost indicator for Solar Water Disinfection (SODIS) keeps advancing. Two of the organizations we are in contact with now have prototypes of electronic indicators and they are currently in talks with investors in order to finance the production of initial series. We hope to see these series produced within a few months so that the first projects in the field can start soon.

In the meantime, we will be working on an alternative approach: We have been contacted by researchers from Queens University in Belfast (Ireland) who are working with materials which change color according to the amount of solar radiation received - for example, a plastic which turns from blue to transparent after some hours in the sun. This mechanism enables users to know immediately if their water bottles have been exposed to sufficient amounts of sunlight in order to be safe for consumption. Our ultimate goal is to have such devices which are re-useable, but for a start we will work with disposable indicators. The informal parthership with this research organization is a great step ahead and we are looking forward to hearing from the first phase of field tests, which is planned to take place in June  - we will keep you updated.

More good news: Until Sunday, May 12, there is a special campaign for gift cards on Global Giving: each supporter who buys a gift card for a loved one or colleague will generate an additional $5 for our project ($5 for each card, that is!). $8,000 are available in matching funds and a $1,000 bonus will be awarded to the project with the most tribute card donors. So please, send a gift card to say Happy Mother's Day or just greet friends and family in the next week to help us reach our target (e-cards and hard copy versions are available - simple choose the "Gift or In-Honor of"-tab in the window with the donation options).

Best regards from the whole project team,

Matthias Saladin

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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