Some SWR» stations have water machines that are also chargeable.
Unless I was pressing the wrong buttons, the one at Bournemouth last year wanted a fee (I can't remember how much).
I Used Guildford again yesterday, excellent machine. Used Southampton last week, good job the train wasn't coming soon, slow? Reading has one which I don't need to use.
The Guildford one is by the toilets on Platform 2 and is activated by putting your bottle near it (no buttons to press). Only issue could be if you had a large diameter bottle. The Reading one in the waiting room on Platform 7 I think was free, but now charges?