Use sunlight to reduce harmful germs in drinking water

Hygiene and sanitation


Save and edit this resource as a Word document

Content: Reduce the number of disease-causing germs in your cooking and drinking water. Put water for your household needs in clear jars and bottles and put them outside in the sun for several hours or the whole day.

Special note: There are some important guidelines to keep in mind when encouraging the use of this method of water purification. Please see notes at the end of the script.

Many serious diseases such as diarrhoea, typhoid, and cholera are caused by germs in dirty drinking water. Thousands of children and adults die from these diseases every year. So it’s important for all of us to have clean drinking water.

Many people boil their water to make it safer to drink. This method of purifying water requires a lot of fuel. Today we’re going to talk about a way to kill germs in water that doesn’t use up firewood. It’s easy. You just put bottles of water in the sunlight and the sun’s rays kill the germs.

Here are the steps to follow. First find the containers (bottles, jars, etc.) you need to hold all the water for cooking and drinking in your household for one or two days. Use colourless or light blue containers made of clear glass or clear plastic. You should be able to see through whatever containers you use. When water is in a pond or stream, the sun’s rays can’t penetrate all of it. But when you put the water in containers, the sun’s rays can penetrate all the water and destroy the germs.

Remove the labels from the bottles and wash the bottles well.

Get your water from the lake, pond, well, or stream where you usually collect water. If you can see lots of dirt particles in the water you will have to get rid of them before you use this method. Some people filter or settle their water to clear it. Others use parts of plants, for example the seeds of the Moringa tree (Moringa oleifera), which can be added to the water to clear it.

When the visible dirt particles are removed, pour the water into the clean bottles. Cover them to keep out dirt and insects. Put the bottles outside in an open space where the sun can shine on them all day. Spread out the individual containers so they don’t shade each other.

It’s a good idea to get into a regular routine for purifying your water. For example, you might put the bottles of water outside every morning at the same time and leave them in the sun until late afternoon. They should stay in the sun for at least about five hours. But if you don’t have much time and you need the water as soon as possible, a couple of hours at midday when the sun is strongest should be enough.

Now you can use the water for cooking or drinking. Use the water directly from the bottle you had in the sun. This way you reduce the chance of more germs getting into the water. Re-use the same containers next time you want to purify water in the sun. There’s no need to wash them again unless they get dirty accidentally.

In summary then, you’ll get the best results if you:

1) use clean, clear bottles that are colourless or light blue

2) take all labels off the bottles

3) make sure there are no visible dirt particles in the water.

4) leave the bottles out in the sun all day. If you need the water sooner, then leave the bottles in the sun for two hours around mid-day when the sun is strongest.


1. Conditions and limitations of this method of disinfecting water using sunlight from the Solar Water Disinfection Workshop, Ste. Anne de Bellevue, Quebec, Canada, August 15 -17, 1988, compiled by Josef Ayoub.

i) This technique is not as effective during periods of constant rainfall and heavy cloud cover.

ii) It is only effective for clear water. Water which has lots of dirt in it (turbid water) cannot be cleaned efficiently with this method. Therefore, turbid water should be treated first by methods such as settling, filtration, and possibly coagulation before using sunlight disinfection.

iii) Water treated by this method should be consumed directly from the container used for exposure to sunshine to avoid recontamination.

iv) It is recommended that this method of disinfecting water be part of an extensive, comprehensive health education program which explains the importance of clean water. Good sanitary practices are important when using this method so that the treated water does not become re-contaminated after treatment.

2. A different method of purifying water is described in another DCFRN item which you may wish to use with this item:

Simple water purification – Package 14, Item 16

Supplement to Item 9

The moringa tree: A multi-purpose tree with seeds that can be used for water purification.

Please note that full information about how to use moringa for water purification is not given here because training is recommended before people start to use the method.

The moringa tree (Moringa oleifera) is a drought-resistant tree which provides nutritious food for people. (Other names for the tree are benzolive, malunggay, kelor, horseradish tree, drumstick tree, and relish tree.) The seeds of the tree can be used to purify water.

Women in parts of Africa, especially the Sudan, have been using the seeds to clarify muddy water for many years. The women dry and then crush the seeds. Then they make a powder and mix it with water. This clears the water and also reduces the number of bacteria in the water that could cause disease. And the powder doesn’t affect the taste of the water.

In the past few years. considerable research has been done on the use of moringa for water purification. Dr. Samia Al Azharia Jahn who works with the Water Purification Project of the German Agency for Technical Cooperation (GTZ) in Germany has been studying moringa and the use of its seeds for purifying water for many years. She thinks that the use of moringa seeds for water purification is appropriate for water treatment in rural areas of tropical countries. However, she says that it is important for women who are going to use them to get training in the method so that they learn how to use them correctly.

The leaves, pods, roots, and fruit of the moringa tree can all be eaten. The leaves contain lots of vitamins and minerals, and both the leaves and fruits have lots of protein. So this tree provides very nutritious food. The blossoms can be eaten in salads or used to make tea, and beekeepers find them to be a good source of nectar for their bees. Moringa trees also make good living fence posts. The tree is easy to grow, grows very fast, and can stand very dry weather.

In item 8 of this package another use for moringa is described under the heading “Moringa leaves control fungus in seedling plants.”

Information sources

1. Solar disinfection of drinking water and oral rehydration solutions: guidelines for household application in developing countries (1984, 56 pages), by Aftim Acra, Aeina Raffoul, and Yester Karahagopian, published for UNICEF, Regional Office for the Middle East and North Africa, Amman, Hashemite Kingdom of Jordan. 

2. Solar water disinfection (1988, 239 pages), Proceedings of a workshop held at the Brace Research Institute, Montreal, Quebec, Canada, August 15 – 17, 1988, edited by T.A. Lawand, R. Alward, O. Odeyemi, J. Hahn, T.C. Kandpal, and J. Ayoub. Published by the International Development Research Centre, Ottawa, Ontario, Canada. 

Other information sources

1. Water purification with Moringa seeds from Dian Desa, Waterlines, Vol. 3, No. 4, April 1985, Intermediate Technology Publications Ltd. 

2. “he tree that purifies water, by Dr. Samia Al Azharia Jahn, Hassan A. Musnad and Henz Burgstaller, Unasylva 152, Vol. 38, pages 23-28, publication of FAO of the United Nations.