Organisation: Ingenieure ohne Grenzen e.V.
Project Partner: Kilimanjaro Childlight Foundation
Project title: Solarthermal Water Disinfection (SoWaDi)
Short Project Description
The project goal is to give people access to germ-free water with the help of a Solarthermal Water Disinfection (SoWaDi)  system developed by the Darmstadt regional group of EWB Germany. This is intended to protect the population from common diseases that can be caused by microbiologically contaminated water. In order to increase the distribution of the system, a free construction manual  was published.
The system developed by SoWaDi disinfects microbiologically contaminated water with the help of solar energy. Neither electrical energy nor chemical additives are used. This is to ensure that the plant can be set up at low cost and at different locations. Therefore, materials are used that are resource-saving, locally available and as inexpensive as possible. The system is designed in such a way that the water to be boiled is heated continuously. Even in the event of a defect, only sufficiently heated water can leave the plant. The construction of the system is designed to be as simple as possible, so that it can be carried out with only a few tools and the construction manual SoWaDi developed. Thus, the installation of the system can be done by the users themselves or with the support of local craftsmen.
The human right to Water and Sanitation is recognized word-wide since 2010, but yet contaminated drinking water is still a major problem in many regions of the world and poses a serious threat to the health of the local population in many countries, especially in large parts of Africa and Southeast Asia. For instance, it is estimated that 829,000 people die each year due to diarrhea related to unsafe drinking water .
In Tanzania, four million people lack access to an improved source of safe water, and 30 million do not have access to improved sanitation . People living under these circumstances have to spend a significant time traveling long distances to collect drinking water or are dependent on water treatment measures. Boiling water is the most widespread method of killing harmful germs and pathogens. However, boiling over a fire is often associated with high energy costs together with environmental and health damage due to deforestation and smoke emissions.
Because of these reasons the SoWaDi project group decided to develop a solar thermal water disinfection system, that boils water through the use of solar energy. The rough goal is to use simple and widespread tools and building materials for the construction to enable the user group to build the system on their own. However, the current test phase is more about considerations of principle. The question of distribution remains unresolved and will be addressed intensively after the current test phase.
The project is implemented and supervised by Engineers Without Borders (EWB)  and its project partner the Kilimanjaro Childlight Foundation (KCF) .
EWB is a registered non-governmental organization. EWB Germany is primarily concerned with engineering activities, training and research in development assistance and development cooperation. The organization consists of engineers who are active in various areas, architects and engineering students, as well as non-engineers like ethnologists or people from other disciplines. The aim of the association is to help people by working with local sovereign project partners and training future users. The financing includes the collection of donations and public subsidies. EWB Germany is organized in regional groups and competence groups.
The Darmstadt regional group supervises and manages this project through the SoWaDi project group. The project group is supported by the competence group for water sanitation and hygiene  and the competence group for renewable energies. The goal of SoWaDi is to provide access to germ-free water for people wherever there are problems with microbiologically contaminated water in the Global South. This should help improve the living conditions of the people and thus strengthen their self-empowerment.
The KCF is a non-governmental organization that aims to help disadvantaged children to a better life and a better future. In their projects, they provide clothing, food, education and medicine in schools and communities. They are also involved in the construction and renovation of schools, orphanages and residential buildings.
Detailed Project Description
Research And Development
The project was initiated in 2011 by the Darmstadt regional group of EWB Germany. The aim is to create an alternative to make water from rainwater cisterns drinkable. After numerous conceptual phases in which thermal simulations were carried out and numerous prototypes were built and tested. There were two opposing prototypes. One was a harp-like absorber with multiple rising pipes and the other one with a meander-shaped absorber. The harp system was discarded in 2013 and the meander-shaped collector was chosen.
The next phase is characterized by a cooperation with a sewage treatment plant in Darmstadt. The aim was to determine the change in water quality before and after passing through the device. For this purpose, microbiologically contaminated water was filled into the system and the boiled water was microbiologically examined after the system had been run through.
After the functioning of the system could be ensured both thermodynamically and microbiologically, a possible implementation could be tested in the subsequent development phase in cooperation with a project partner in Tanzania. For this purpose, two devices were built by vocational students of the Malage Vocational Training Centre with the support of an EWB project team. It should be emphasized that the materials were all available locally. On the other hand, the construction of the devices was difficult to implement with only a construction manual. With the experiences of the implementation phase from 2017, the device was further developed, and the first version of the construction manual was published in 2020.
In addition, technical problems that arose during the construction of the devices in Tanzania could be solved. The devices from 2017 were repaired and brought up to date. In the current test phase (as of December 2020), the project team is trying to collect as much data as possible about the use, quality and durability of the device in order to be able to ensure clear communication regarding how the device works in a subsequent distribution phase. For this reason, a test facility was set up in Darmstadt, Germany in 2019.
The microbiologically contaminated water is transported through a narrow pipe from the input tank to the collection tank which’s opening is positioned higher than the unheated water level in the pipe. The entire system has approximate dimensions of 2.7 meters x 2 meters x 2 meters. It has an inclined part that is called the absorber and collects the solar radiation. In the absorber the water is heated to boiling point by solar thermal energy. It is therefore important for the process that this part of the device is well insulated. The resulting steam bubbles push the water at boiling point out of the riser pipe into the collection tank . As hot water flows into the collection tank new microbiologically contaminated water from the input tank flows into the absorber. Since the principle of operation is based on the displacement of the water vapour and not on gravity, it can be ensured that the water does not simply flow through the system. New water constantly flows into the absorber pipes, as the system is based on the principle of communicating vessels . Communicating vessels are vessels that are open at the top but connected at the bottom. A homogeneous liquid stands at the same height inside the vessel because gravity and air pressure are constant.
Since the water cooled down, it must first be heated again. However, the time for this process is reduced after the device has started up in the morning hours. The treated water should be consumed within a day. Due to the collection concept developed by the regional group, only boiled and thus microbiologically uncontaminated water is transported from the flat-plate collector to the collection tank. The result is not distilled water, but microbiologically uncontaminated water. Therefore, minerals, but also other substances, such as chemical residues, are still present in the water.
It is important to ensure that water is available in the input tank at all times, as the system could overheat very quickly without water. To finish the process, it is sufficient to cover the absorber.
For more detailed information, you can look at the references in the appendix.
Due to the problems in the target countries, the SoWaDi project of EWB is therefore concerned with the development of a small-scale solar thermal system for the treatment of rainwater. In order to determine its functionality, a prototype in Germany was examined more closely by operating the system with heavily contaminated water. This treated water was then analysed in more detail. The focus of the analysis was on the elimination rate of the pathogenic indicator organisms E. coli and total coliforms. In addition, the parameters pH value, electrical conductivity, temperature, water hardness, dissolved organic carbon and turbidity were also considered. In none of the 35 measurements could pathogens be detected in the effluent. Furthermore, high turbidity values and a comparatively high-water hardness did not lead to complications. Thus, the system can be considered suitable for decentralised drinking water treatment. However, the use of copper as pipe material as well as the first daily produced water volume turned out to be potential weak points. Currently, the input and output of the plant is tested three times a year for various things. For example, in addition to E. coli, the water is tested to see if it is turbid or contains copper. Regarding copper, it is tested whether copper ions dissolve, which would be negative for health in the long run.
At the moment, six systems are installed in Tanzania, as well as a test system in Germany (Darmstadt)  The devices are mainly used in private households but also in schools. So far, all plants have been built for test purposes. Therefore, all these plants have been financed by Engineers Without Borders. However, in the long term, it should be possible to finance plants through private means. For instance, this can be done through a microfinance system.
With normal solar radiation, the average water output of the system is 20 liters per day, making it particularly suitable for use within small family groups. The average costs per system is approximately 250 euros. However, the price can vary greatly due to process- or site-specific conditions. For example, in the case of devices at elementary schools, it must be ensured that children do not have any access to the devices. Therefore, there are higher requirements in terms of safety in this case. In general, the acceptance of the SoWaDi system is high in the regions where it is used. On the positive side, it is easy for people to have access to clean drinking water without the risk of disease or diarrhea. The water treatment with SoWaDi devices turns out to be simple because the only effort is to fill up the tanks of the device and to ensure that maintenance work is carried out regularly. This includes, for example, that the window and container are cleaned regularly, and that occasional maintenance work is carried out. Compared to conventional water treatment by boiling, there is no need to collect firewood. This gives a time advantage, because some time can be saved and used otherwise. Another advantage of the SoWaDi system is that there are no operating costs for its operation. So far, the maintenance of the device could be done on-site by the locals, which is also a positive point.
The long-term goal is to further spread and create more SoWaDi devices. For this reason, the current test phase is intended to collect as much data as possible on the use, quality, and durability of the devices. For this reason, a test facility was set up in Darmstadt, Germany in 2019. The aim is to collect long-term data so that technical optimizations can be tested more easily, and the efficiency of the system can be increased. In addition to the device in Germany, four more devices were built in Tanzania in 2020 so that the data is more diversified. In the coming years, the goal is to build and analyze even more test devices before the they become widespread.
Working principles 
Product data sheet 
- ↑ https://www.sowadi.de/en/
- ↑ https://www.sowadi.de/wp-content/uploads/2020/08/ConstructionManual_Version_2020_01-1.pdf
- ↑ https://www.who.int/news-room/fact-sheets/detail/drinking-water
- ↑ https://water.org/our-impact/where-we-work/tanzania/
- ↑ https://ingenieure-ohne-grenzen.org/en
- ↑ https://www.kilimanjarochildlight.org/
- ↑ https://ingenieure-ohne-grenzen.org/de/wash
- ↑ https://www.sowadi.de/en/device/how-it-works/
- ↑ https://www.sowadi.de/en/project/technical-concept/
- ↑ https://www.sowadi.de/projekt/aktuelle-anlagen/
- ↑ https://www.sowadi.de/wp-content/uploads/2020/11/Funktionsweise_new_eng.pdf
- ↑ https://www.sowadi.de/wp-content/uploads/2020/09/Projektdatenblatt_DEU-IOG02_202009_eng.pdf