usually seldom wash car it will cause that water spot. Try best practice usually after rain try not to leave it dry. wipe it with microfiber. (concentrate on the mirrors top of the car..bonnet and hud) when the sun comes these water will be like a magnifying glass.   it will cause burn and thus leave water marks. or easier and faster way. use leaf blower to dry it.

my gf is very lazy to wash car person...her car full of water spot...all mirrors is like crying mark...u know how she wash car? she use water....just spray on the car....then leave it overnight without wiping it. after spray water on it. she thought drive it off the water will go away. yes it will but the access water that stick around will have a chance to make your windows and car paint severe water mark when the sun comes up...

u mention that is around 8 months... if u hardworking try wash one week once or twice. one year two times of clay. every two months once wax. even three month once wax also ok. it will prevent water mark from occurring. if my explanation wrong please correct me sifu KC.