The requirements could vary from human consumption to ultra pure water needed for modern electronics. The various levels of water qualities are achieved by applying certain processes. A brief description of this process is given below:

This process is basically used for removal of suspended matter in equipments known as clarifiers. Clarifiers provide adequate storage time so that the rising water velocity is less than the settling velocity of water particles. The suspended matter settle down as sludge and this is removed intermittently or continuously. Sometimes, coagulants and flocculating agents are added to increase the settling rate and achieve better separations. Conventional clarifiers are circular structures. Recently, inclined plate / tubular structures are used for clarification to save space.

If higher degree of purification is desired, a demineralization plant consisting of at least a cation exchanger vessel followed by an anion exchanger vessel will be required. The cation exchanger resins exchange Ca ++, Mg++, Na++, ions for H+ ions and the anion exchanger resins exchange HCO3 -, Cl -, SO4 -- ions for OH - ions resulting in the production of salt free water . Presently more than one type of resins are available and given the chemical composition of water, a flow sheet can be developed for an optimum treatment of water. When the alkalinity of water is high, degasser units are employed to save on the cost of alkali regenerant. To obtain very high purity water, mixed bed polishers are employed at the end of the chain. Employment of mixed beds are necessary to obtain low conductivity and low silica levels in the treated water.

Condensate polishers are again mixed resin bed polishers operating at higher velocities and pressures to achieve higher throughputs at the same obtaining the required purity of treated water.