That's a really popular idea on the internet because it's very easy to grasp, but the numbers don't work out well. The weights you can actually lift aren't much compared to the volume of a reservoir of water, and the heights you can lift them are but a fraction of the thousands of meters being discussed here. Yes, the concrete isn't going to require much maintenance, but the gearboxes needed are a significant engineering challenge. Pumping water or compressing air are a lot easier, and batteries are going to be hard to beat.