Boiling water is by far the easiest way to make water that has been contaminated by microrganisms safe for drinking. There's not much you can do about chemical contaminants like heavy metals, unless you have some serious equipment, but for making water collected from your roof, from a creek, or the stored water that you forgot about for a few years drinkable, you just can't go past a good boil.
You don't even have to boil it for any length of time. If you happen to have a thermometer, you could have your water at 70 degrees C for 30 minutes, and that would kill everything. If you bring the temperature up to 85 degrees, then it's good after just 3 minutes. So by the time you've actually got the water up to the boiling point, everything was probably dead a minute ago, and the time it takes to get the water back down to a temperature that's drinkable without burning your mouth, you've killed everything several times over.
However, if you haven't got any way to heat your water, you can resort to household bleach.
BUT - and there's a definite "but" here.
Check the label on your bleach first!
Household bleach is typically between 5 percent and 6 percent chlorine. Check how strong your particular brand is. The table below gives the amounts of 5-6% chlorine bleach solution to add to how much water - it's really not a lot!
Also, not all bleach is just bleach. There's a massive proliferation of household cleaners out there, and they are not all the same. Some of them contain dyes, some contain perfumes, and some contain detergents and other additives which can be seriously not good for you, even in the small amounts you'd be using. Always read the label first, and if it's unclear as to what else has been added to the bleach, don't use it in your water.
Mix your plain unscented bleach with the water thoroughly and then leave it for at least 30 minutes before using (60 minutes if the water is cloudy or very cold) to let the approriate chemical reactions do their thing.
Another point to note - Cryptosporidium (a rather nasty diarrhea-causing pathogen) is highly resistant to chlorine, so if you are aware that it's a potential contaminant, boiling is always the best option.
Treating Water with a 5-6 Percent Liquid Chlorine Bleach Solution
|Volume of Water to be Treated||Treating Clear/Cloudy Water: |
Bleach Solution to Add
|Treating Cloudy, Very Cold, or Surface Water: Bleach Solution to Add|
|1 litres||3 drops||5 drops|
|2 litres||5 drops||10 drops|
|4 litres||1/8 teaspoon||1/4 teaspoon|
|20 litres||1/2 teaspoon||1 teaspoon|
|40 litres||1 teaspoon||2 teaspoons|