Tldr? Why would anyone do this? To what end?
You can do this with a long enough hose and height difference by just using river water
Why not set something up by the river instead and just route the power?
what? Something like a Water Mill? You are crazy!
To utilize power that is otherwise wasted? The water can still be used in the garden etc. Also if there is a power cut the water often keeps running, so you could use this to charge a small battery or a phone.
If the power goes out you’d probably be better off using solar or a even gas. Maybe if you’re using water for something else anyways it makes sense but how much power can really be generated by turning a house on for a min? How much water is wasted?
Given most of water comes from public facilities it is structurally just unsanctioned and ineffective transmission of power from shared pump to private generator. Would be a simple energy theft if you didnt pay for water. A waste of water and energy anyway.