Why Nairobi water taps will continue to be dry

Most water taps in Nairobi remain dry after the shutdown of Ng'ethu treatment works four days ago due to high turbidity of raw water from the Aberdares catchment area.

The shutdown, which the Nairobi City Water and Sewerage Company on Friday said would last a few hours, was to "avoid the transmission of water that does not meet the World Health Organisation standards".

Turbidity is the quality of being cloudy, opaque, or thick with suspended matter." Its measurement is a key test of water quality.

The company explained, “There has been increased river flow causing very high turbidity in the raw water, which is flowing slurry and is suspected to be caused by a landslide upstream."

NCWSC production manager Philip Githinji told the Star on Monday that the situation is “fluid.” Ng'ethu's treatment capacity is 18,333 cubic metres cubic per hour or 440,000 cubic metres per day.

“We are treating water from 11pm at 90 per cent of the capacity to comply with quality standards set by the regulator,” Githinji said.

"We are dealing with very high turbidity of above 5,000 NTU (Nephelometric Turbidity Units) causing us to temporarily shut the systems then resume once turbidity goes down," he said.

The normal raw water quality for 85 per cent turbidity is below 100 NTUs.

WHO requires portable water to be below five NTUs after treatment.

Githinji said conventional water treatment system like Ng’ethu treats up to 800 NTUs.

The problem started last week with Friday and Saturday being the worst days.

“There was a landslide in Njabini in 2012, forcing water schemes to shut down because water mixed with soil,” Githinji said, adding that they now have to contend with turbidity from the landslide site as well as that from road runoff and slopy land.

On Friday, the NCWSC said slurry (semi-liquid mixture of suspended particles in water) was being brought to the treatment plant.

"The raw water flowing into the treatment plant has failed to respond to several types of chemical treatment and solutions are underway to ensure the treatment process is operational and normalised," the company said.

Ng’ethu serves 85 per cent of Nairobi with water. The rest of the supply comes from Sasumua, Kikuyu Springs and Ruiru dam. These are not affected. 

The shutdown has affected the City Centre, University of Nairobi main campus, Coca Cola factory, Jomo Kenyatta International Airport, EPZ-Athi River, South B, South C and the neighbourhoods.

The Industrial Area, Mlango Kubwa, Mathare, Eastleigh, Moi Airbase, Huruma, Kariobangi and Pangani are also affected.

The others are Maringo, Buruburu, Bahati, Outer-Ring, Baba Dogo, Dandora, Dandora KCC factory, Umoja, Donholm, Fedha, Tassia, Avenue Park, Nyayo and Embakasi.

The taps were also dry in Ruai, Njiru, Kayole, Komarock, Kenya Breweries, Kenyatta University, Kahawa Barracks, Kasarani, Mwiki, Kahawa Sukari, Garden and Thome estates.

The areas affected on Limuru Road are Parklands, Ngara, Aga Khan Hospital, University of Nairobi's School of Law, City Park, Gigiri, United Nations and Muthaiga.

- mwaniki fm