SO-lar DIS-infection of water.
I’ve always been an advocate of boiling water.
Somehow I’ve got fixated with the fact that it’s a rare bug that can survive boiling.
Yet, here I am, in the UK, writing about using PET 2 liter lemonade bottles and the sun to disinfect water.

SODIS Principles. (They aren’t even hard to understand).


  • Fill a clear, clean, 2 liter PET bottle (think lemonade bottle)
  • With clear (low turbidity i.e. no color or bits) water,
  • Initially filling the bottle to 2/3 capacity, shaking it like mad for 20 seconds to pump air into it, (Some bugs hate Oxygen)
  • Then complete the fill to the top, and screw on the cap.
  • Leave in the bright sun preferably on a shiny surface like a corrugated roof or in a silver lined ‘solar’ collector
    (Caution now kicks in because of living on this little island paradise latitude 50-57 1/2 degrees North) for 2 full days.
    As it gets cloudy in the UK and never as hot as the tropics.

Water now safe to drink.
The system works, the figures prove it, even if the weather is cloudy . Apparently the usual storage methods can be applied now i.e. Hydrogen Peroxide or Chlorine Bleach to keep things “nice”.
Back to chemicals, ho-hum!


Is it REALLY possible to SODIS in the UK?
Wading through 4 MB of impressive research from in Switzerland the answer for me is PROBABLY.

What, no better than probably? I feel that is an appropriate answer because of our lousy climate.

This year it’s been a good summer, plenty of sunshine BUT rarely has the ambient temperature been above 20 Celsius.

SODIS works in two ways as far as I can tell.

  1. The UV side of the light attacks the living bugs at a cellular level and certainly Crypto and Giardia don’t like a suntan. That I like!
  2. Sunlight heats the water. Bugs and heat don’t mix. This is where I feel uneasy as although Crypto and Giardia would ruin my day, it’s everything else I worry about like Hepatitis, HIV, and Leptospirosis. Let alone the common disaster bugs like cholera. Them? Well them can ruin my life.

Hence my love of giving bugs
a nice hot bath in the billy can.

And finally.
I’m all for alternative ways to treat water and am not a fan of chemicals. I can’t afford portable reverse osmosis pumps preferring low tech silvered ceramic to stop the Giardia and Crypto.

However, it’s the tiniest little things in life that cause the most harm (after all it was bacteria that killed the Martians in “War of the Worlds”) so not being too worried about destroying the ozone, I’m still going to boil.

It’s winter (in case no one noticed) so I’m now collecting rainwater directly from a plastic sheet into my water bottle.
Am I still boiling that? YOU BET!

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2 Responses to SODIS

  1. equippedcat says:

    Hmmm. I have a black painted stainless steel water bottle here in the desert. The bugs would not get the benefit of the UV, but I bet the water would get pretty hot. Perhaps so hot the plastic cap would be at risk?

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