Water Supply Process - Purify raw water from surface or underground water sources

The objective of a municipal water supply plant is to treat and purify raw water drawn from approved surface or underground water sources to obtain potable water that complies with purity standards set by the government and distribute the potable water to households and industries for their use. ( The water drawn is not wastewater but raw water) There are various techniques used in the industry for the treatment and purification of raw water but generally a water supply process will have the following steps: collection, mixing and flocculation, sedimentation, filtration and disinfection.

(1) Collection
Raw water is obtained from either surface water sources such as lakes and rivers or underground water sources. Surface water sources have to be approved by the government which set stringent criteria such as COD content, proximity to heavy industries, etc.

(2) Mixing and flocculation
The main impurities present in raw water are floating solids, colloids and soluble microscopic
particles. The mixing and flocculation process involves the addition of coagulation chemical agents such as bitter salt, benzotrichloride and aluminium sulphate. These coagulation agents will react with the colloids causing them to stick together to form clumps which can then be easily removed through the sedimentation process.




(3) Sedimentation
Following the mixing and flocculation process, the raw water will be pumped into large water tanks known as clarifiers whereby non-soluble particles such as sand, mud particles and the clumps will form a “sludge blanket”. As these non-soluble particles and solid clumps are heavier than water, the blanket will sink to the bottom and as it does, the blanket works like a finely-meshed net to catch other smaller particles. The water at the top of the tank, now free of solids, overflows to the gutter-like spokes at the top of the tanks.

(4) Filtration
Water is then transferred into the filtration basins whereby soluble microscopic particles will be
removed. At the bottom of each filtration basin are layers of coarse sand, fine sand and activated carbon. As the water seeps down through these layers of sand and coal, tiny particles as small as
one micron are left behind. The activated carbon also has the ability to remove tiny particles and also chemical compounds that affect the water’s taste and odor.

(5) Disinfection
The filtered water then goes through a final disinfection whereby chlorine and chloramine are
added to kill any bacteria or viruses that may be present in the pipes from the plant to the final
user. Water is also checked for purity level for consumption before it is pumped out for residential and industrial use.