This study assesses the business case for the creation of the Upper Tana-Nairobi Water Fund to help protect and restore the quality and supply of water to one of Kenya’s most productive and economically important regions. The Upper Tana River basin covers approximately 17,000 km2 and is home to 5.3 million people. The water it provides is of critical importance to the Kenyan economy. It fuels one of the country’s most important agricultural areas, provides half of the country’s hydropower output, and supplies 95% of Nairobi’s water. It is also home to areas of unique biodiversity and iconic national parks.