It's very easy to get bogged down on this issue which is what has happened in my home town of Bradford on Avon, where the Town Council secured funding for 3 new water fountains months ago, and even bought the fountains, but none are yet operating because they have tied themselves up in red tape.
The station at BoA^» (Bradford-on-Avon - next trains) must have a water supply from which staff fill their kettle, and fitting an outside tap is a few hours work for a plumber.
There are always reasons not to do things but we need to cut through the red tape and just do it on some issues.
If we want more people to travel by rail, which is absolutely the right way to go compared to travelling by car, we need to make life easy and promote the full range of environmental measures to help people make the right choices.
ps. thank you for letting me post on this issue!

Many people travelling by train are choosing to do so, rather than by car, for environmental reasons, and are also very switched on to the "plastic-free" message. However few if any stations have a tap where people can easily fill up a water bottle. It would be great if each station had an easily accessible tap for drinking water. It doesn't need to be a complicated fountain, just an outside tap, and if there is concern about water wastage, staff could turn the supply off overnight.