Kenya – Sasumua

Designing equitable payments for watershed services at the Sasumua watershed

Sasumua dam is located at the southern ridges of Kenya’s Aberdare Mountains. It provides the capital, Nairobi, with 20% of its fresh water needs. However, economic activities around the dam’s catchment are causing sedimentation and contamination by water pollutants.


PHOTO by Mwangi Gathenya

The Sasumua dam catchment covers approximately 107 square kilometres, of which 50% is under cultivation. The catchment has a high population which is growing at 3.5% annually. The average farm size is 2.86 acres. Polluted runoff from small towns and farms results in high turbidity, high bacterial count and high water treatment costs.

The major pollutants are biological and soil materials from agricultural fields, coliform bacteria from human and animal waste, and heavy metal ions from roads and garages. In some spots, the concentrations of heavy metals are close to World Health Organization limits.

PRESA is working in partnership with the Jomo Kenyatta University of Agriculture and Technology (JKUAT) and the Macaulay Land Use Research Institute.

PRESA delineated the Sasumua watershed and identified hotspot areas responsible for most of the sedimentation.

We projected that the annual costs of water purification will rise up to US$178,560 over the next ten years if farming practices continue as they are. This problem can be solved by developing partnerships with land owners to implement sustainable land management practices such as terraces, contour farming, grass filter strips and grass waterways.

What would these partnerships look like?

For instance, implementing a grassed waterway approximately 20 kilometres long and 3 metres wide can reduce soil sedimentation by 20%. This can save $23,000 a year in water purification costs.

Nairobi water users are willing to pay an increased tariff. This therefore looks like a simple business case. However:

To harmonise the positions of land owners and potential beneficiaries of watershed services, PRESA convened a meeting of Sasumua stakeholders during which there was agreement to pilot a rewards-based approach for watershed management under WRMA.

Next steps

PRESA will seek to generate lessons from activities at Sasumua

Site profile

[mappress mapid=”6″]

Environmental service

Watershed services

Potential provider of environmental services

Owners of agricultural land in about 50% of the watershed.

Potential buyers

  • Nairobi City Water & Sewerage Company
  • Private sector companies, as part of corporate social responsibility.