The African Development Bank (AfDB) says it is in talks to finance the downstream water supply, irrigation and power components of the Thwake Multipurpose Dam, as construction of the main structure on the Makueni-Kitui border reached 94.2 percent completion.
The commitment was made during a site visit on Thursday, October 15, according to The Star and Water News Kenya. Construction had slowed for nearly two years because of a funding gap before the lender stepped in with an additional Sh10.6 billion.
“As a Bank, we will ensure the project reaches completion and achieves the benefits. This means provision of water for food security; implementation of the irrigation component, water supply and sanitation for residents and hydropower for energy generation,” said Mtchera Chirwa, the AfDB director for water and sanitation.
Water impoundment targeted for January
Water Secretary Samuel Alima said work had resumed after the shortfall was addressed. The remaining works focus on the concrete face slab and a bridge linking the two counties across the dam.
“The contractor has resumed with the concrete face already having some panels, while others are also under preparation. They have also started doing the bridge,” Alima said.
The Ministry of Water, Sanitation and Irrigation is targeting water impoundment by the end of January 2027, followed by commissioning in April 2027. The ministry said the timeline depends on the completion of outstanding works.
How the funding is structured
In June 2026, the AfDB approved €68.39 million in additional financing for the first phase of the programme. This comprised a €64.20 million loan from the African Development Bank and €4.2 million from the African Development Fund. The Kenyan government committed €15 million in counterpart funding.
The first phase is estimated to cost Sh42.4 billion, according to official project records cited by The Star, with the AfDB and the government sharing the cost. The original design put the cost of the full four-phase programme at 487 million units of account, an AfDB accounting unit whose value moves with exchange rates.
A 688 million cubic metre reservoir
The 80.5-metre-high concrete-faced rockfill dam is being built at the confluence of the Athi and Thwake rivers. It is designed to hold about 688 million cubic metres of water, making it one of Kenya’s largest reservoirs. It covers about 9,217 acres and has a catchment area of about 10,276 square kilometres.
The wider programme has four parts: the dam itself, hydropower generation, water supply and sanitation, and irrigation.
The water supply component is designed to deliver about 150,000 cubic metres of treated water a day to about 1.3 million people in Makueni and Kitui counties, as well as Konza Technopolis in Machakos County.
The plans also include a 20-megawatt hydropower plant and an irrigation scheme covering up to 40,000 hectares, or about 100,000 acres, of farmland in the semi-arid Lower Eastern region.
The dam is also expected to regulate flows along the Athi River, reducing flood risk downstream and supporting water availability during dry spells.
Treatment plants, transmission pipelines and distribution networks still have to be financed and built before households receive water from the reservoir.
Alima said separate work to clean up the Nairobi River system, including sewage collection, wastewater treatment and river widening, was under way to improve the quality of water flowing into the Athi.
