Water's boiling point is 212 degrees Fahrenheit, so water must be at least that hot to sterilize. Water needs to be boiling in order to become sterilized.
For purposes of sterilizing water that is not safe to drink, simply boiling the water kills most bacteria and viruses. However, boiling water does not effectively kill prions and fungal spores, so boiling water is not the most effective means for sterilizing food.
If water must be sterilized but cannot be boiled, bleach can be used to clean the water. The Environmental Protection Agency recommends using 1/8 teaspoon of bleach per gallon of water and to let the water stand for 30 minutes after mixing before use.