The purification of water when only unclean water is available or when the available drinking water is believed to be contaminated. One of the following methods may be used: 1. Water is strained through a filter and boiled vigorously for 30 min. 2. Three drops of alcoholic solution of iodine are added to each quart (approx. 1 L) of water. The water is then mixed well and left to stand for 30 min before using. 3. Ten drops of 1% chlorine bleach, 2 drops of 4% to 6% chlorine bleach, or 1 drop of 7% to 10% chlorine bleach is added to each quart (liter) of water. The water is then mixed well and left to stand for 30 min. If the water is cloudy to begin with, double the amount of chlorine is used.