How will plastic balls help prevent water evaporation in our dams?

Evaporation, Water Loss, It is massively expensive to cover dams and reservoirs with sheeting/roofs in order to prevent water loss through evaporation. So when the wind blows as hot as it has in Cape Town the past few days, millions of liters of water is lost through evaporation. Is there something we can do about it, or is this a natural phenomenon that we just need to accept?

The City of Los Angeles has come up with a unique methodĀ of minimizingĀ that cost and yet still preventing evaporation through the deployment of 96 Million “shade balls” in reservoirs outside the city. The shade balls are black, hollow, plastic balls, filled with fresh water, treated against UV ray deterioration and purported to last 25 years, although they will be recycled well before then. These balls float on the waters surface, block out the suns light and in addition to stopping evaporation, also prevent algae growth.

Evaporation, Water Loss

The figures look impressive: instead of spending $300 million on building a roof, the city spent less than $35 million on shade balls. 1.1 Million cubic meters of water will be saved annually through this work and could well lead to more cities following their lead, and more water being saved.

Should Cape Town follow suit?