I appreciate some of your points. I had to look up how many days it rains here (not easy to guess) and it turns out to about 30% of days (reference).
I can't give stats for everyone in the country but in my house, with 2 people, we each cycle a lot and take a shower every day with at least one bath a week. We do a couple of loads of laundry and all the normal washing/cooking/toilet flushing you expect. We collect rain for usage in the garden but importantly we have plants adapted to the local climate. We use 60L/person/day i.e. less than one sixth of a Californian. If I had a moderate pool (say 5x3x2m i.e. 30,000L, 8000 US gallons or 24 milliacre feet), that means that I could drain it and re-fill it completely every 2 months and still come in under a Californian usage. Surely most pools don't need much maintenance water provided they are covered when not used?