Largely advocated for developing countries, solar water disinfection is gaining some traction in the survival skills crowd. Imagine an end to boiling your water in order to make it safe. Consider how nice it would be to no longer need expensive water filtration devices or potentially toxic water-treatment chemicals. Sounds great, right? Too good to be true, even…
In reality, solar water disinfection (SODIS) really is a good fit for equatorial countries with abundant strong sunlight and few other resources. This water treatment method simply uses the sun’s energy for disinfection. The most common technique is to expose plastic bottles full of contaminated water to the sun for a minimum of one day. The sun’s abundant UV light kills or damages almost all biological hazards in the water. The advantages to this way of treating water are plentiful. It’s easy; it’s inexpensive or free; it offers good (but not complete or guaranteed) bacterial and viral disinfection. Furthermore, the method uses no dangerous chemicals and it does not require constant attention.
Now for the bad news. You need sunny weather, or two days of overcast sky, to reach the maximum effectiveness. SODIS becomes less effective as you travel away from the equator. You cannot use it in rain; it offers no residual disinfection; it may be less effective against bacterial spores and cyst stages of some parasites (similar to chlorine); and the water and the bottle need to be clear. If that wasn’t bad enough, this method does nothing to help with chemical contamination, and only small bottles can be processed (the bottle must be 2 liters or smaller). If you have a clear glass bottle, it should last for years. But if the bottle is scratched up or made from milky plastic, less sunlight gets through, making this method more questionable.
Is SODIS better than nothing? Sure, this method is reducing dysentery and deaths related to poor water quality around the world. But for me and my own, I’ll stick to my boiling pot, MicroPur tablets, and Katadyn filter all the same.