Yes you are providing a hang-out for pool players, if the venue, lets say in this guys case is a league, and the league dues require them to pay league dues, and if someone chooses not to buy anything, which is not uncommon for pool players, since most are cheap, they do not have to buy anything. Charging for free water, is a great way to make sure that you get NO BUSINESS and to piss off potential people who might come back and spend money later.
I know I would be pissed if someone tried to sell me water, as for a water cooler that is free, thats fine too, it works, and it fullfills a basic need water.
What's going to happen next, are people going to get charged to go to the bathroom?
Pool players hang-out, thats part of the culture, thats the way things are, they watch and hang out, they are not required to pay for anything. And if your a room owner and start becoming nit picky, like I have seem some room owners get, you will drive more customers away, and you will gain a reputation that is not wanted.
Just give them the water, and be happy, and thankful that they came into your place, and filled the parking lot, and made your place look popular. Just because one of a bunch wont buy anything does not mean that some others won't, its a part of doing business. Just like some will tip and some wont, serve them all as if they were your best customers, do not pick and choose to serve better tippers than non tippers, you do not have to be happy about them not tipping, but a tip is not required.
My point is serve all people the same, equally, treat them all with respect even if some do not buy, do not make people pay for water...
Come up with a better idea than that for sure....!