How is sewage and wastewater treated?

If your water comes from a surface-water source, such as a river or lake, some work must be done to get rid of particulate matter. Often water is withdrawn and pumped into holding ponds or containers, where solids and particles can settle to the bottom. Possibly filters and sand beds are used to screen out particulate matter, and at a minimum, chlorine is added to kill dangerous bacteria and microorganisms.