Anything suitable. Bus shelters, a tunnel on a children’s playground, the overhang of a village hall, pub garden... If not wet then anywhere outdoors is fine, you just need somewhere discrete off the road. Rural Bus shelters can work. But generally you’ll look at the map in advance and work out roughly where the dozies might strike and what’s around on or just off the route.
As to water, two water bottles should see you 2 hours in really hot weather and anything up to 3-4 hours in cooler conditions. Even in the most rural places you will pass places to top up water, shops, churchyard or cemetery taps, public toilets, pubs etc..