If water is polluted (cloudy or you have reason to believe it has been contaminated in some fashion even though it looks clean), strain it through paper towels, coffee filters or several layers of clean cloth. This will remove sediment and anything floating. Bring the water to a boil (it will bubble vigorously) and let it remain so for five minutes (or longer if you have the heat to spare).
If you have no heat source, strain the water as explained above and then add liquid chlorine household bleach or tincture of iodine (do not use granulated forms of bleach as they may be poisonous). Stir or shake well and let it stand 30 minutes before using.
Buy an eyedropper to make this easier and use it for this purpose only. Here are the formulas:
Amount of Chlorine Amount of Bleach to add to: Iodine Amount of Clear Cloudy Clear Water Water Water Water One quart 2 drops 4 drops 3 drops One gallon 8 drops 16 drops 12 drops Five gallons 1/2 teaspoon 1 teaspoon 3/4 teaspoon
Tincture of to add to: Amount of Cloudy Water Water One quart 6 drops One gallon 24 drops Five gallons 1 1/2 teaspoon
Source: Lafferty & Associates, Inc.