National Program for Sustainable Irrigation Fact sheet 2005/4 As much as 40% of water stored in a farm dam can be lost through evaporation, depending on the depth of the dam and its surface area. Dam design can significantly decrease evaporation by reducing the surface area to volume ratio (deeper, narrower dams) and planting windbreaks to provide shade and reduce wind turbulence. Over the years, a number of commercial products have also been developed to minimise water losses, including floating plastic covers and chemical products that change the