Evaporation can be reduced by ...

Evaporation can be reduced by either providing some sort of a barrier between the water and the air or by somehow slowing the movement of the air near the water surface. Planting a wind-break of trees and shrubs around the dam will help to some extent

1. By additive.
2. By Keeping Free Water Surface Area Minimum: Reservoirs and lakes are the water bodies with large surface area.
3. By Spreading Surface Films on the Reservoirs and Lakes
4. By Providing Mulch on the Land Surfaces:

Calcium hydroxide (hydrated Lime Ca(OH2)), food grade stearyl alcohol (C18H37OH, commonly referred to as octadecanol) and cetyl alcohol (C16H33OH, commonly referred to as hexadecanol) that can reduce surface water evaporation by 20-50% without negative environmental impacts. It is an odourless white powder that automatically and quickly spreads into an invisible, molecule-thin film over the surface of water. It is an internationally patented

Shade balls are small plastic spheres floated on top of a reservoir for environmental reasons, including to slow evaporation and prevent sunlight from causing reactions among chemical compounds present in the water.