Solar water purifier (SODIS)
Clear bottles of water left in the Sun for 6 hours link energy to clean drinking water.
The big idea
Sunlight can make water safer to drink. It costs nothing and uses only clear plastic bottles.
You will need
Tick things off as you gather them.
Step by step
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Step 1: Prepare the bottles
Peel off the labels. Wash the bottles. Use only clear bottles that were used for water or soft drinks.
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Step 2: Clear the water
If the water looks cloudy or muddy, pour it through a clean cloth first. SODIS works only on fairly clear water.
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Step 3: Fill and shake
Fill each bottle three quarters full. Cap it and shake hard for 20 seconds so air mixes in. Then fill the bottle to the top and cap it.
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Step 4: Lay them in the Sun
Place the bottles on their sides on a metal roof, or on foil, in full sun. The metal sends extra heat and light onto them.
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Step 5: Wait six hours
Leave the bottles for about 6 hours in strong sun. If the sky is cloudy for most of the day, leave them for two days.
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Step 6: Check the temperature
If you have a thermometer, measure the water. It will have warmed. Let it cool before drinking.
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Step 7: Store it safely
Keep the treated water in its bottle, capped, and pour straight into a clean cup.
What to look for
- The water gets noticeably warm.
- Clear bottles on a metal sheet heat fastest.
- Muddy water is much harder to treat.
Why it works
Sunlight carries a kind of light called ultraviolet, or UV-A, that harms the tiny germs in water. The heat helps too. Together, six hours in the Sun can kill many of the germs that cause stomach illness. Shaking adds oxygen, which helps the process. SODIS does not remove chemicals, so it is only for water that looks clean but may carry germs.
Try this next
- Compare water in a clear bottle with water in a green or scratched one.
- Measure how warm the water gets each hour.
- Find out how many people in your area do not have safe drinking water.
Stay safe
SODIS treats germs only. It does not remove chemicals, salt or dirt. Do not use water from polluted sources. Use bottles only for water.
Link to the grid
Clean water and clean energy are linked. Pumping and treating water takes electricity, and the Sun can do some of that work for free.
Learn how the grid worksMore sun power experiments
Mini solar panel circuit
A small solar panel lights an LED or spins a toy motor. Test it in sun, in shade and at different angles.
Solar cooker
A cardboard box, foil and plastic wrap trap the Sun's heat. Melt chocolate, warm water or cook rice.
Solar water heater
Black-painted bottles or pipe in the Sun heat water. Measure the temperature as it rises.