How is water treated?

How is it treated?

In order to make this water safe to drink, it undergoes a treatment process which is tailored to suit the source of where the water is taken from. For example, ground water requires much less treatment than river water. At the treatment works water may go through many stages of treatment such as filtration, clarification and disinfection.

Clarification - A chemical is added to raw water and combines with material such as algae and silt to form larger particles. These are then removed either by settling them out (sedimentation) or by using air to float them to the surface (flotation).
Filtration - This process removes any particles remaining in the water after clarification. The water flows through a bed of sand or other media where the particles become trapped. It is necessary to ensure that as many particles as possible are removed in order for the final disinfection stage to be effective. It is at this stage that harmful microorganisms are removed.
Disinfection - In this country, chlorine is the most common method of disinfection. It is essential for the removal of bacteria from water. Water companies add enough chlorine to ensure that the water is kept safe in its journey to your tap.
The levels of organic substances such as pesticides and herbicides are controlled by a combination of ozonation and carbon adsorption. The ozone breaks down the chemicals which are then adsorbed onto the carbon.
Nitrate levels in water are controlled by a process called ion exchange which is a similar process to that used in domestic water softeners. Nitrates are removed in this process.
Lead treatment - Water companies in some areas also treat the water which is leaving the treatment works to prevent it picking up lead from the pipes in your home.