Much much more trivial to look at a map and see a big blue pool than try to parse water bill differences. Having had a pool, there isn't an obvious pattern as to when i had to fill it up, etc.
Low hanging fruit are the ones that aren't covered.
I would assume watering a garden consumes more than a swimming pool.
Gardens must be taxed too then.
Watering plants with a watering can? Absolutely not. Watering a grass lawn to lush greenness, with a hosepipe? Agreed that uses a lot of water.