Here is what the State of Washington says about purifying water:
Purifying by boiling
If your tap water is unsafe, boiling is the best method to kill disease-causing organisms.
If tap water is unavailable, the following may be considered as potential water sources. Water taken from these sources should be boiled before drinking.
Rainwater
Lakes
Rivers and streams
Natural springs
Ponds
Caution: Many chemical pollutants will not be removed by boiling.
Cloudy water should be filtered before boiling. Filter cloudy water using coffee filters, paper towels, cheesecloth or a cotton plug in a funnel.
Bring the water to a rolling boil for at least one full minute.
Let the water cool before drinking.
Add two drops of household bleach per gallon to maintain water quality while in storage.
Purifying by adding liquid chlorine bleach
Treat water by adding liquid household bleach, such as Clorox or Purex.
Household bleach is typically between 5.25 percent and 8.25 percent chlorine. Read the label.
Avoid using bleaches that contain perfumes, dyes and other additives. Be sure to read the label.
Cloudy water should be filtered before adding bleach.
Place the water in a clean container. Add the amount of bleach according to the table below.
Mix thoroughly and let stand for at least 60 minutes before drinking.
Treating water with household bleach containing 5.25-8.25 percent chlorine
Volume of Water to be Treated Bleach Solution to Add
1 quart/1 liter 5 drops
1/2 gallon/2 quarts/2 liters 10 drops
1 gallon 1/4 teaspoon
5 gallons 1 teaspoon
10 gallons 2 teaspoons
Caution: Bleach will not kill some disease-causing organisms commonly found in surface water. Bleach will not remove chemical pollutants.
DOH Pub 821-031
Revised - July 2013