The EPA has established guidelines for water purifiers. Some water filters only remove protozoa, which are the largest. Though some also remove bacteria, viruses are too small to be physically removed by filters, so a chemical disinfectant is typically included. Water filters vary considerably in cost, speed, capacity and ease of cleaning, so shop carefully to find one that meets EPA requirements and suits your needs and budget. Follow the manufacturer's directions for using, cleaning and storing your filter.
Chlorine bleach is ideal for treating water.
The American Red Cross recommends that you bring water to a rolling boil for one minute. After that, add 16 drops of liquid chlorine bleach per gallon of water, then stir. Make sure that the only ingredient in the bleach is 5.25 percent sodium hydrochloride and that there are no added fragrances or soap. Let the treated water stand for 30 minutes. If it smells of chlorine, it is safe to drink.