I am curious as to how utility companies or water companies filter and purify water for drinking. Specifically, I am most curious as to how water companies filter and purify water for drinking that is taken from rivers. My hometown is Huntsville, AL, and Huntsville Utilities provides the drinking water in Huntsville. I know that Huntsville Utilities gets most of the water it provides for drinking from the Tennessee River. How do water companies typically filter out the debris that inevitably must come in with the river water? I suppose a water company could use giant metal screens to filter out things like twigs and tree branches, but how does the water company filter out things like grains of sand or other small particles. I know that the water companies use chlorine to purify water for drinking. Chlorine would probably kill all the microbes, but how do water companies remove chemical pollutants from drinking water?