So long as you dont use hose pipe to connect from the mains you are ok. Push fit, or fixed pipes from main is fine. And once its been filtered, its no longer classes as tap water, as its an "altered substance". Also, our tanks in vans isnt connected to mains, so isnt classes under hose pipe ban.
Apparently drought bans dont affect us....but could imagine customers complaining about us wasting water, esp on down stairs.