Use the Sun to Treat Your Water

     I knew you could use some special UV ray water treatment system to purify water but I didn’t realize you could use the sun to do the same.  I came across an article describing the process of taking water from a stream and placing it in a clear plastic bottle in the sun for 6 hours and having it be safe to drink afterwards.

     Who knew sun exposure could kill parasites, viruses and bacteria?  Not me!  Here’s how…


How to Purify Water with Sunlight

April 19, 2012, by Ken Jorgustin

UV-A rays from the sun, (Ultraviolet-A, longwave, 315-400 nm), will terminate harmful bacteria, parasites, and viruses in water, given enough sun exposure.

A clear plastic bottle filled with water, exposed to the sun for 6 hours will make the water safe to drink (see the caveat list). In fact, the effectiveness of terminating  harmful bacteria is an amazing 5-Nines, that is, 99.999 percent!

The recommended bottle to use is a “PET” bottle. It is very common and is typically used for soda or other soft drinks.

PET, PolyEthylene Terephthalate, Recycle code #1 on bottom of bottle.

The bottle must not be colored. It must be a clear bottle. Again, it must be a clear plastic bottle. Not glass (glass blocks too much of the UV-A for this purpose).

The bottle must be clean. Common Sense.

Know your water source (as best you can)… if you believe it to be chemically toxic, don’t use it.

Fill the bottle with water. If the water is very cloudy, it must be filtered by first pouring through a cloth or such material to capture sediment.

Lay the bottle down in the sun. Do not stand them up. Ideally the bottles would by placed so that they face the the sun at a similar angle, to maximize the UV-A penetration.

Even better… lie the bottles on a reflective surface to increase the UV-A exposure using direct and reflected sunlight. This is not necessary, however it would shorten the required time and ensure optimum UV-A exposure.

If the sky is partly cloudy with only a few clouds, then 6 hours sunlight exposure will be enough. If the sky is half filled with clouds, or more, then 2 days will be required.

Note that the outdoor temperature does not matter, so long as the UV-A sunlight exposure has been 6 hours.

List of germs that are terminated from UV-A sunlight exposure at 6 hours

  • Bacteria – Escherichia coli

  • Bacteria – Vibrio cholera

  • Bacteria – Salmonella

  • Bacteria – Shigella flexneri

  • Bacteria – Campylobacter jejuni

  • Bacteria – Yersinia enterocolitica

  • Virus – Rotavirus

  • Parasites – Giardia

  • Parasites – Cryptosporidium (needs 10 hours exposure)


List of caveats to UV-A sunlight water purification

  • This method kills germs. If the water is already contaminated with chemicals from pollution, the chemicals will remain.

  • If the water is cloudy and dirty, it should be filtered first to allow the UV-A rays to effectively penetrate into the water.

  • The plastic water bottle should be no bigger than 2 liters. In moderately cloudy water, UV-A will lose 50 percent effectiveness at a depth of 10 mm (about 0.5 inch), whereas UV-A will only lose 25 percent effectiveness at a depth of 10 mm in clear water. Just use a typical size soda bottle or water bottle.