1. Rainwater. 2. Springs. 3. Rivers and lakes. 4. Surface wells. 5. Deep or artesian wells.

Rain water takes up the dust and gases from the air, and organic matter from the roofs over which it is collected. The long storing in a cistern gives bacteria opportunity to grow in large numbers, causing the water to be unsafe for drinking purposes.

Springs are a source of pure water supply if they are not contaminated by passing through soil which is polluted.

Rivers and lakes are a common source of water supply, but they may be made very unfit for drinking if the surface water and sewage from towns and cities is allowed to drain into them.

Surface wells are a very unsafe source of drinking water supply, and the water should never be used when there are cesspools, drains, barnyards, or any other sources of contamination within a radius of 200 feet of them.

Deep artesian wells furnish pure water as a rule, unless the piping is not tightly jointed, when impure water from a subsoil stream near the surface may enter the pipes.

Ice

Freezing has little effect upon bacteria except to lessen temporarily their vitality. When the ice melts, the bacteria may again become active. Ice made by artificial means from distilled water is the only pure ice. For cooling drinking water, the water should be placed on the ice and the ice should not be put into the water.

Hard And Soft Water

Soft water is water in which no mineral matter is dissolved. Hard water is water in which such minerals as lime, magnesium, and iron are dissolved. Boiling precipitates some of the mineral matter, thus tending to soften the water. This mineral deposit may be seen on the inside of a teakettle. Hard water that is to be used for cleansing purposes may be softened by the addition of washing soda, borax, ammonia, potash, or soda lye.