I've got a 5 year old 5 stage RO system. I'd like to start using RO
water to make beer but the 3.2 gallon tank takes two days to deliver
the 5 gallons of purified water necessary for a single batch of beer.
That's assuming I don't try to make a pitcher of iced tea while I'm
waiting, which can add yet another day. Needless to say, I need to
make a change. Would a 14 gallon tank allow me to draw 5 gallons of
purified water at one time? FWIW, I have a 100gpd TFC membrane,
which I assume is up to the task. If so what's a good source for
pressure tanks at reasonable prices? Online is fine, but what kind
of brick-and-mortar stores sell parts like this?

Other suggestions?