The Northern Water Collector Tunnel, set for completion in March 2020, will be the longest water tunnel in Kenya.
It is aimed at boosting water at the Ndakaini Dam and increasing water supply to Nairobi by 140 million litres per day.
The project that started on February 24, 2015 and whose phase one comprises the construction of an 11.8km diameter water diversion tunnel from Maragua River to Ndakaini Dam, will be complete by March next year with the government hailing the project as one of its kind.
For the first time, water will be transported underground without interfering with the general environment.
According to Athi Water Services Board Chief Executive Officer Mwangi Thuita, the tunnel will solve a lot of challenges experienced in the water and energy sectors which are affected by terrain.
"Some places are 250 metres high and that would be quite challenging to pump water up and down unlike the tunnel which is able to transport and pump water in a challenging terrain," he said.
While explaining the technical perspective of the project, China Gezhouba Group Company says the project has been done with strict adherence to Kenya's environmental laws and policies.
Mr Dong Qide, the project engineer, said the excavation of the tunnel involves the construction of three intakes of Maragua, Gikigie and Irate.
Flood water from the three rivers will be intercepted and diverted to the tunnel and then to Ndakaini Dam before being transported to Nairobi.