How is Water Purified in Water Treatment Plants? Which Type of Water needs Urgent Treatment?

-Usually, Groundwater is Pure to an Extent but Surface Water needs Treatment: 1. Water goes through a Wire Mesh and then through Sand and Gravel. This is Filtration 2. Iron Sulphate or Aluminium Sulphate added to Water allowing Fine Particles to Clump Together and Settle. This is Sedimentation 3. Chlorination, or UV Light, or even Ozone, will be Used to Kill Microbes.