Two forms of water supplies exist in the world: surface water and ground water. Surface water is that which is found in rivers, streams, reservoirs, and so on. Ground water is that which is extracted from the ground using deep or shallow wells. The impurities in these two water supplies varies, depending on the environment where these waters occur.

Both surface water and ground water supplies are subject to impurities - chemicals that dissolved or combine with water to affect the composition of these water supplies. For example, the extensive contact with the earth's atmosphere produces a greater effect of gases on surface water supplies, while the earth formations contacting the ground water supplies provide a greater amount of mineral components.

Depending on their chemical composition, the presence of these impurities in water supplies affects water usage by causing hazards such as corrosion and/or mineral deposits. Treatment of water to eliminate or, at least reduce, the destructive results of water impurities requires careful consideration of several factors of water chemistry.