[sho]

In other words, you would need such a ridiculously large tower that the idea is not really viable. 3 tons of water for 80 watt hours? That's 37kg of water per watt hour. I use more like 4 kilowatt hours in a night; that's almost 150 tons! You're starting to talk about a serious, and seriously expensive, engineering project.

Maybe it would be viable if you lived next to a convenient cliff or other ready structure to simply place a big tank on top of with a pipe hanging down but if you actually have to build the structure yourself it sounds like a non starter. And that's without even considering the other engineering hassles you'd have, like corrosion, filtering seawater, maintenance, etc.