That’s an interesting idea. Storing a tank of water is a lot more straightforward and efficient than generating electricity off-peak and storing it in a bank of lead-acid batteries.
I’ve recently set up a website for a guy who sells a commercial rampump, mostly to dairy farmers in the Waikato region (https://williamsonrampump.co.nz). He had a promotional video done about fifteen years ago and it’s looking a bit old now but a fair number of those pumps are still running. I got given the rather difficult task of converting that old video tape to a digital format (DVD and web video). It was a mission even getting the capture card to track the signal properly.
It’s interesting to see all the different designs out there too. Some of them look pretty dodgy though. I saw a design using PVC pipe on another website, I don’t know how long that would last. I’d expect it to start coming apart in less than six months from the hammering they get.