Water; it's the most important substance on earth. Without it, we wouldn't survive. it's also helped power our lives for more than a century. More than 6 percent of our nation's electricity comes from hydropower. And as wind and solar power continue to grow, water can also play an important role in bringing more renewable resources on to the power grid. One way is by storing energy through a technology known as pumped-storage hydropower. Think of it as a big battery, flexible enough to respond to various power demands. When the sun is shining and the wind is blowing, electricity is in high supply, so water is pumped up to higher elevation reservoirs during this time. When the sun goes down or the wind stops blowing, water is released back to lower reservoirs, basically filling in the gaps during peak demand and generating the needed electricity. Pumped-storage is the most dominant form of energy storage on the electric grid today. There's more than 21 gigawatts of storage capacity already installed in the United States, with future opportunities to more than double that, keeping the grid reliable and ready to add more renewable electricity to the mix at low operating costs.