There shouldn’t be a water shortage in Nairobi

 By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

03 April 2011

During the past one month, I have been getting water in my house only once a week: from late Monday evening to early Tuesday morning. As my family adjusts its consumption patterns, I can’t help but think about the numbers at play.

Now, my household comprises of three adults and two children. Our average monthly consumption is between 10 and 20 cubic metres – one cubic metre is equivalent to 1,000 litres.

Therefore, on average, my household consumes about 15,000L of water per month. It comes to about 500L per day. This is our “unhindered” consumption when we are not bending over backwards to save the precious liquid.

If we assume that all other people in Nairobi use water at the same rate, what would be the daily total requirement for the city? The first step is to work out the average consumption per person. This is simply 500L divided by the 5 persons in my house. The result is about 100L per person per day.

Next, we multiply this by the city population of about 3.2 million (according to the 2009 population census). At 100L per person, the total requirement for domestic use should be 320 million litres or 320ML (Note that the “M” here is capitalised – a small “m” would mean “milli”!).

Let’s not forget that there is also a significant number of “migrants” who come to the city to work during the day only and they don’t sleep here. UN-Habitat estimates this number to be about 1.5 million.

Since they are here for only half the day, and they do their washing in their home towns, we can assign them about 30L of Nairobi’s water. This is about one-third of what an “indigenous” Nairobian consumes.

Therefore, the migrants consume about 45ML of water daily. Adding this to the indigenous consumption brings the total requirement comes to about 365ML.

How does this compare with the supply?

The bulk of Nairobi water comes from the Ndakaini dam, but not directly. It is first pumped to the Ng’ethu Treatment Works for purification and then piped down to the city residents.

The Ng’ethu Treatment Works has an installed capacity of about 525,000 cubic metres (that is, 525 million litres) per day. However, the normal operating output is 440ML daily – you don’t drive your car at full speed either, do you?

Therefore, there is a surplus of 75ML and consequently, we shouldn’t be experiencing any shortages. Perhaps it’s because we have not included industrial consumption: but most heavy consumers of water have sunk boreholes.

In addition, a large proportion of the city residents don’t have piped water in their houses. Therefore they consume much less the 100L we have used in the calculation.

Therefore, the above calculation is fairly accurate. So, with a 75ML surplus, I can’t understand why I haven’t been getting water continuously?