Water cost about £1.30 per cubic meter which is a 1000 litres and about the same again for drainage.
How many 1000 litres do you use?
I wouldn't be telling a customer there's an extra charge for the water surly that's an overhead to your business which is part of the quoting process.
By the same token if some numptyblett said you not using their water because of a meter I wouldn't be bothered doing the job, sure sign of things to come.
Regards
Graham