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Plant that cleans Ruiru’s water

The various basins and storage units that comprise the Ruiru water treatment plant. [PHOTO: STANLEY WAITAGEI/STANDARD]

At the heart of Ruiru is a water treatment plant that has been in operation for the past 16 years.

According to the plant’s technician, John Letumta, they generate safe drinking water for the populace by treating water from Ruiru River.

“Water contamination can occur both at the surface and in the ground. If the pipes are not properly protected from contaminants, the quality of water suffers. Improper storage can also result in unsafe drinking water,” he says.

To prevent this, Letumta says they follow specific steps that ensure the final output is safe for human consumption.

They start by adding chlorine to the raw water as it enters the plant from its source — Ruiru river.

“Doing this kills micro-organisms such as bacteria, protozoa and viruses that may cause illness. It also prevents growth of algae at the treatment plant which would make the water stink and taste bad,” Letumta says.

Once this is done, aluminum sulphate is added which works by destabilising natural fine matter suspended in the water. “We use mechanical mixers to do this process known as rapid mixing and once water goes through, it passes on to basins where it is stirred gently. This makes all the small particles collide, stick together and grow into a size that will readily settle,” he says.

After this, the water is passed through sedimentation basins where all the particles settle at the bottom. The clear water then goes through filtration where it is passed through a bed of sand and gravel which removes particles of suspended matter and traps them in sand.

“Filters must be cleaned periodically since particles trapped in them reduce the rate of filtration. The process of cleaning filters is known as back-wash and is achieved by forcing clean water through the sand to remove particles that are deposited in the waste drains,” Letumta said.

Additional chlorine is then added to the water as it leaves the treatment plant in preparation to go to consumers.

To prevent the water from corroding water plumbing materials such as copper, brass, lead or other metallic materials, lime is added into water just before it is released to the distribution system.

“We use Magadi soda ash (sodium carbonate) as lime,” Letumta says noting if the mentioned water treatment process is followed to the letter the populace is assured of getting clean, safe water for domestic use.