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 surface characteristics of the water and reduce evaporation. Research was undertaken by the National Program for Sustainable Irrigation's predecessor (the National Program for Irrigation Research and Development) in 2002 to assess these products. This fact sheet captures the key findings, which show that their effectiveness can depend on a combination of cost, durability and their vulnerability to being disturbed by the wind and associated wave action.