Hi Dave,
Congratulations on you new arrival
Well if your doing traditional, which I guess you are then all you need to do is fill your bucket up 3/4 to start the day off and keep an eye on your water level, when it get down to the last 1/4 refill it with customers outside tap. If they are in ask if not just fill up. If you're not sure about you can do this then take a couple of 25ltr cans with you. If space is tight try a collapsable water barrel, caravan suppliers sell them or Millets.
A tip for ya, if your using you car and you don't want the bucket spilling everywhere, place an old tyre in your boot and use that for holding the bucket still, works a treat!
Anyway, good luck, keep posting if you want any advice.
Regards, Trev