Nairobi, Kenya, has a growing water crisis. The conversion of forests and wetlands to agricultural uses in the Upper Tana River catchment, which supplies Nairobi’s water, has led to heavy sedimentation in the river, reducing the capacity of reservoirs and increasing the cost of water treatment—by up to 30 percent during heavy storm periods. During drought periods, on the other hand, the Nairobi government has had to implement water rationing, with some residents finding their taps turned off entirely for days at a time1, forcing them to buy water from unlicensed vendors at marked-up prices.
Nairobi’s problems are not unique: nearly half of all cities around the world experience periodic water scarcity, and cities that rely on surface water are particularly vulnerable. Poorly managed land development can lead to heavy runoff laden with sediment and fertilizer, polluting the rivers and lakes that cities rely on for water. These pollutants are expensive to filter and can reduce water availability during droughts. And as the world’s population grows and concentrates in cities, not only will demand for water itself increase, but a projected 10 percent increase in cropland over the next 15 years could lead to more pollution and sedimentation, further reducing supplies and increasing expenses.
Cities can improve their water by investing in nature-based solutions within water catchments that protect water before it reaches their outskirts. A healthy water catchment serves as a natural filter, removing sediments and nutrient pollution long before they enter the pipes and reservoirs that bring water to cities. Investing in the health of catchments can also offer a range of co-benefits, improving the livelihoods and well-being of those living within source catchments, and protecting the fish and wildlife that inhabit these ecosystems.
The Nature Conservancy’s Urban Water Blueprint2 maps out the global potential for addressing the growing urban water challenge through nature-based strategies. Focusing primarily on the world’s 100 largest cities, this report found that more than 700 million people globally could benefit from improved water security through catchment conservation. One strategy to carry out this work is through water funds.
Water funds provide a mechanism for downstream users to directly or indirectly compensate upstream users for activities that deliver water benefits to the payer. Public and private water users, including businesses and local governments, invest collectively in conservation of the catchments from which they source their water. Many cities are coming to see these funds as a way to minimize treatment costs and reduce the chance of water shortages in the future.
The Urban Water Blueprint identifies five strategies water users can invest in to reduce sedimentation and nutrient pollution and improve their water security: forest protection, reforestation, agricultural best management practices, riparian restoration and forest fuel reduction. Each strategy has costs and benefits, and different strategies will make more sense in different catchments. Agricultural best management practices, such as the use of terraces and cover crops, have the broadest applicability across our sample of cities, potentially improving water quality for 85 million people. Forest protection and restoration—while spatially more limited in their applicability—could achieve reductions in pollution that would benefit up to 52 and 11 million people, respectively.
The Conservancy is working with 60 water funds around the world, in different stages of development and operation. While the majority of water funds are currently located throughout Latin America, new regional versions of the Urban Water Blueprint show great promise for establishing water funds in China and Sub-Saharan Africa. The recently released Sub-Saharan Africa Urban Water Blueprint3 identified 28 cities that could improve their water security by investing in conservation activities, benefiting more than 80 million people.