California has the most residential pools of all the states - over 1.5 million inground and aboveground units.
PDF warning: http://www.apsp.org/Portals/0/2016%20Website%20Changes/2015%...
PDF warning: http://www.apsp.org/Portals/0/2016%20Website%20Changes/2015%...
https://en.wikipedia.org/wiki/List_of_states_and_territories...
Might be more fruitful to look at a per-capita metric?
As in, it's not uncommon to live here and not know anyone with a pool.