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NCWSC Water treatment process

Raw Water is drawn from Rivers into Ndakaini Dam and water then released to Ngethu Treatment plant.  By gravity, water flows through intake tunnels into a distribution chamber in the plant’s raw water building. Vertical pumps draw the water through a series of traveling screens, which prevent large debris, such as fish and seaweed, from entering the system. It is then pumped to the main treatment plant to begin the treatment process.

The water flows through rapid mixers where polyaluminum chloride is added. The chemical reaction causes dirt, clay, and bacteria to form a product known as floc, which settles easily out of water. In flocculation basins, large paddles gently stir the water causing the floc to increase in size and density helping it to settle at the bottom of the basin.

Next the water flows to settling basins. The sludge at the bottom of the basin is removed by scrapers and sent to the waste water system.

The partially treated water flows to the filter beds. Chlorine is added to the water for disinfection. The water flows through layers of sand, gravel, and anthracite coal. The filters remove particles, such as viruses, cysts, bacteria and any remaining floc.

Filters are cleaned by backwashing, in which clean water removes the collected sludge from the top of the filter to settling clarifiers. When the backwash water settles, the clear water is recycled back into the water treatment process and the sludge is removed.

Before water enters the distribution system, more chlorine is added to prevent bacteria build up. Fluoride is also added to fight tooth decay. Caustic soda is added to neutralize the acidity and prevent the corrosion of pipes. Finally, high service pumps push the treated water from a clear well reservoir into the distribution system.

NCWSC maintains a rigorous purification program that meets and/or exceeds the regulations set by the WHO, KEBS, and the Department of Health.

Water quality is strictly monitored at the NCWSC laboratories to make sure the water is safe and clean to drink. Highly trained chemists test for bacteria, pH levels, turbidity, chlorine residual and other related analysis.

The NCWSC conducts more than 70,000 tests annually to make sure all necessary drinking water regulations are met.

For more information on water treatment contact:

The Production Manager,
Nairobi Water Company,
P.O. Box 30656-00100,
Ng’ethu Treatment Works
Tel:  020-3542500/672978

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