I think this a really cool low-tech idea: black plastic balls added to Los Angeles’s largest reservoir to prevent algal blooms and limit evaporation.

The concept is ingeniously simple. The black balls floating on the water prevent most of the sunlight from reaching the water, reducing the light’s reaction with bromide and chlorine in the water which can form bromate (a suspected carcinogen) and, more importantly, helping to prevent algae from growing, which is the great water quality scourge of surface water sources. The presence of the balls is also expected to slow down evaporation, saving about 300 million gallons a year. During a drought, every little bit helps…