How to clean water using plastic bottles and the sun

Developed in Switzerland, low cost method can clean bacteria from water and you don’t need to buy a thing

The evils of plastic water, microplastics, and beverage bottles have already been noted in previous Green Prophet articles, including one dealing with bottled water conflicting with green values ; and another more recent one that noted how so-called bottled water is really mostly tap water that is bottled and then sold at premium prices.

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But now, there may be some redemption for that one-and-a-half  liter polystyrene bottle as a safe and low cost way to purify drinking water. Known as solar disinfection, or SODIS  for short, the method is almost cost-free and is now being used in many developing countries to make well and tap water safe for human consumption.

How to purify water using plastic bottles

The SODIS purification process involves filling a number of one and a half or 2 liter plastic bottles about 3/4 full of clear water (if the available water is cloudy, it should first be filtered through a layer of sand).

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The bottle is then shaken vigorously to mix sufficient air with the water, and then filled to the top with more water and closed. The filled bottles are then placed on a metal or concrete surface (like the roof of a building or house) and left in the sun for at least 6 hours, or until hot to the touch.

The bottles should then be taken inside and allowed to cool before being opened for use.

The SODIS water purification process utilizes the sun’s ultraviolet rays to purify the water, killing harmful bacterial growth and other disease causing organisms. While heating water in plastic is not a great idea, this solution might be worthwhile to save lives.

To enable the water to heat faster, paint one side of the bottle black and then place the bottle on a roof or other surface with the black side down. This acts like a miniature sun boiler, and works on a similar principle as solar water heater collecting plates.

Many Middle Eastern countries have serious water problems.  Some of them, including Iraq, Jordan and the Palestinian Authority (especially Gaza), have dire shortages of safe drinking water, especially in Gaza’s case. The use of this very inexpensive way of water purification by people living in these locations  considerably lessens the dangers of a number of water borne diseases such as cholera and dysentery.

The SODIS method of disinfecting drinking water was discovered at a Swiss research institute, The Swiss Federal Institute of Aquatic Science and Technology.

Although the technology has been known for some time, it’s only been given real media attention in the last year or so. But now, it appears that this very effective and low cost method of purifying drinking water may become a Godsend in parts of the world that are simply too poor to use more sophisticated methods of making water safe to drink.

So if you happen to live in an area with problems of  having enough safe drinking water, don’t throw those plastic water bottles away – they may also be used for  purifying  your water supply, and thus solve their recycling problem at the same time.

Updated June, 2026

::The Sodis Method