The city of Los Angeles in the US has a new tool in its fight against a serious drought.
96 million 'shade balls' have been tipped into three big lakes, or reservoirs, that hold water for the city to drink and use.
When it's hot, lots of water is lost through a process called 'evaporation'.
When water on the surface is warmed by the Sun it floats into the air.
By covering the surface, the balls stop heat from the sun getting to the water.
It's hoped the shade balls could stop up to 300 million gallons of water escaping from LA reservoirs every year.
The balls also protect the water from being polluted by dust and chemicals.