Water Purification takes 5 steps. The 1st is coagulation. The 2nd step is sedimentation. The 3rd step is Filtration. The 4th step is Disinfection. The last step is storage. It normally starts when you flush a toilet. The water goes in to the pipes to an underground machine that takes out the the yucky stuff from the water. Then it goes to a water treatment plant where the take out the hard stuff from the water. Then it gets filtered to get rid of the bacteria in the water. then they disinfect the water to get rid of whatever bacteria is left. Then the water gets stored for dinking and other uses. Here is a picture on the 5 steps. 
