A study by Colombo-based International Water Management Institute (IWMI) fusing ancient technology and modern science explored this balancing act. Hydrological models of the Malwatu Oya basin, and its multiple tank cascades, and the Kalu Ganga basin, with its single reservoir, simulated river flows and estimated how different reservoir types would impact how much water is available, and at which time, for people as well as ecosystems.
The results illustrated ways in which the number, size, location, water withdrawals and water releases of reservoirs in different parts of a river basin can be orchestrated to make reservoir development more holistically sustainable. The right mix can maximise benefits from storage while minimising negative impacts on aquatic ecosystems and ecosystem services.
Population pressure and increasing water competition in a changing climate require us to take stock of the availability and use of water across scales. Water availability not only influences farmers’ commercial prospects but also irrigation-related enterprises and agri-businesses. Greater water scarcity could jeopardize irrigation and agricultural markets while excessive water use can lead to declining ecosystems, water quality and soil health. IWMI advises development partners and the public and private sectors on all aspects of water resource availability and use through a variety of advanced modeling and remote-sensing products and tools, including 
The ability of farmers to engage in or expand irrigation depends on the prevailing socioeconomic, ecological and political contexts, which are often complex, non-linear and changeable. Overcoming systemic barriers to farmer-led irrigation development while taking advantage of existing opportunities 
A lack of affordable credit, particularly for women and resource-poor farmers, is one of the main barriers to expanding farmer-led irrigation in low- and middle-income countries. But 
Scaling farmer-led irrigation requires strengthening human capacity and knowledge exchange among all actors and stakeholders involved. IWMI takes an action research approach, working with national and international research institutions, governments, extension agents and public and private organizations to co-develop the scaling ecosystem and strengthen capacity to drive scaling networks and collective action. We support the