its water getting black due to brake dust. Not a new issue to be worry of. Our brake pads make black powder kinda dust which spread all over the rims . In your case you have emotion variant so you have steel rims on your car which hide brake dust. If you observe a linea/punto with alloys you'll notice that black kinda powder on rims. When you wash them of it looks like black water. Dont worry your car is OK!