This is an interesting question and there is a lot of misunderstanding out there as to how long you need to boil water to make it safe to drink. First, let me say that boiling is the best way to make your water safe to drink. The problem with it is, boiling requires a lot of fuel which might not be readily available in an emergency and it takes a lot of time to boil the water and allow it to cool.
I have heard and read all kinds of recommendations on how long to boil water, such as “10 minutes with a rolling boil” or “3 minutes with a rolling boil”. The truth is as soon as your water hits the boiling point, it is safe to drink. No need to allow it to boil for a period of time afterward. Depending on the altitude, the boiling point is 212 degrees more or less. That temperature is well beyond the point where micro-organisms have been eliminated.
So, no need to boil your water for extended periods of time and waste water (through excessive evaporation) and fuel. Once the water hits a rolling boil it is safe.
Pocket Disaster Survival Guide