Generally water from aquifers is already of high quality because it has been filtered through many layers of chalk or sand and needs only disinfection with chlorine.
Water from rivers and reservoirs contains a range of substances which need to be removed through several processes.
See below to find out how a typical water treatment plant works:
- A series of coarse meshes remove debris such as leaves and plant fragments.
- A chemically active form of oxygen, ozone, is passed through the water to destroy micro-organisma and oxidise metals.
- An approved chemical is added to the water to act as a binding agent for particles and precipitate dissolved metals and to remove organic matter.
- The coagulated particles are separated from the water to form a sludge. The sludge is removed for disposal and the clarified water passes to the filters.
- The clarified water passes through sand and gravel which removes any remaining particles. Filtered water is clean and colourless.
- Pesticide removal
- Granular activated carbon filters. Sometimes used in association with ozone treatment.
- pH correction
- The water's pH value can be altered with chemicals to reduce corrosion and to make the water more stable.
- Phosphate dosing (PO³)
- Phosphate can be added to reduce the dissolution of lead from old pipes.
- The water has chlorine added for disinfection and to reduce the risk of contamination in the distribution system.
- The water is passed through a strong ultraviolet light for disinfection.