Nairobi is approaching the limits of its water supply.
As the city expands, demand continues to rise while the capital remains heavily dependent on rivers originating in surrounding counties. Groundwater has increasingly been used to bridge the shortfall, but boreholes are not a long-term solution. If Nairobi’s water future is to remain secure, the rivers that supply the city must be protected at their source.
Over the past decade, despite mounting pressure on water supply and increasingly unpredictable rainfall patterns, Nairobi’s taps have not run dry. That resilience is not accidental. It reflects sustained investment and collaboration to restore and protect the Upper Tana watershed, the landscape where 95% of Nairobi’s water begins its journey. One of the outcomes has been 42 million litres more water flowing to Nairobi each day than was 10 years ago.
Stretching across Murang’a, Nyeri, Nyandarua, and Laikipia counties, the Upper Tana basin plays a critical role in Kenya’s economy. It quenches Nairobi while supporting rural households, agricultural production, and 65% of the country’s hydropower generation. What happens on farms, forests, and riverbanks in these upstream areas directly affects the reliability, quality, and cost of water delivered downstream.
A decade ago, the warning signs were already clear. Soil erosion, land degradation, and climate variability were undermining farm productivity while increasing sediment loads in rivers and reservoirs that supply Nairobi. Farmers faced declining soil fertility. Local communities drew dirty water, water utilities saw rising treatment costs, as reservoirs filled with sediment. Meanwhile, concerns grew about the long-term reliability of the city’s water supply.
The response required a shift in thinking. The solution was not simply to build more infrastructure downstream. Scientific analysis showed that restoring upstream landscapes could deliver greater value at lower cost. Investing USD 10 million over ten years in watershed restoration was projected to generate more than double that amount in avoided costs and additional power and community benefits.
In 2015, government agencies, water utilities, private sector partners, and community organizations came together to act at the source. Their collaboration led to the creation of the Upper Tana Nairobi Water Fund (UTNWF), Africa’s first water fund built on a public-private partnership model. The concept had already proven successful in the city of Quito, Ecuador in Latin America where The Nature Conservancy helped pioneer the approach. The principle was straightforward. Address problems upstream rather than pay to repair the consequences downstream.
Since then, the fund has supported farmers across the watershed to adopt practical land management measures that strengthen both productivity and water security. These include terracing, agroforestry, grass strips, and the protection of riparian zones along rivers and streams. Such practices help hold soil in place, improve water infiltration, and reduce sediment flowing into rivers.
Farmers have also been supported to construct thousands of water pans that capture rainwater and surface runoff for use during dry periods. This reduces pressure on rivers while strengthening resilience during droughts.
The scale of the work over the past decade has been significant. More than 260,000 farmers have been reached through the program. 470,000 hectares of farmland are now under improved management practices. More than 5.9 million trees have been planted to stabilize soils and restore degraded land, while 980 kilometers of riparian areas have been protected to safeguard waterways.
These landscape-scale improvements have delivered tangible benefits for both rural communities and urban water users.
From the beginning, the water fund model has emphasized shared responsibility. Government provided policy support and early financing. Private sector partners contributed funding to protect the reliability of water supplies on which their operations depend. Farmers themselves invested labour and co-financing, often covering between 20 and 50 percent of the costs of on-farm improvements. This ensured that conservation measures also strengthened agricultural productivity and household incomes.
The economic impact has been substantial. Investments linked to improved farming systems and agricultural value chains have generated significant income across the watershed. Fruit production alone has generated more than USD 117 million over the past decade. In addition, more than 22,000 green jobs have been created. These outcomes demonstrate that environmental conservation and economic opportunity can advance together.
At the same time, sediment risks to rivers and reservoirs serving Nairobi have declined by 41%, helping to protect the performance and lifespan of dams, pipelines, and treatment plants that form the backbone of the city’s water system.
Nairobi’s increasing reliance on expensive groundwater illustrates why this upstream work matters. Aquifers are replenished by rainfall infiltrating through soils and vegetation across the watershed. Healthy landscapes allow water to soak into the ground and recharge underground reserves. Degraded land accelerates runoff and reduces the amount of water that enters the aquifers.
Without sustained watershed management, Nairobi risks replacing one form of water stress with another.
To secure the long-term sustainability of these efforts, the Upper Tana Nairobi Water Fund Trust has been established as an independent institution dedicated to protecting the watershed. The trust provides a long-term platform for partnerships, financing, and coordinated action focused on safeguarding water resources.
Watershed restoration should be recognized for what it truly is: infrastructure investment.
The forests, soils, and rivers of the Upper Tana perform functions that engineered systems alone cannot replicate. They store rainfall, filter water, regulate river flows, and strengthen resilience to droughts and floods. Protecting these natural systems safeguards the billions invested in dams, pipelines, and treatment facilities while supporting rural livelihoods and climate adaptation.
The Upper Tana experience also offers lessons for other African cities facing similar pressures of rapid urban growth and climate variability. Water security cannot be achieved through engineering alone. It requires sustained investment in the landscapes that generate water and in the communities who steward them.
The future of Nairobi’s water supply begins far upstream. And protecting that source must remain a national priority.
Ademola Ajagbe is Regional Managing Director of The Nature Conservancy’s Africa Program.
Eddy Njoroge is a Trustee and President of the Upper Tana-Nairobi Water Fund Trust.
