Water at airports has been around since 2017, according to wayback machine. The purpose is, in the words of its creator:

I created this website because not only am I fed up with paying high prices for drinking water in airport departure lounges, but we all need to cut down on the amount of one use plastics we are throwing away into the environment.

Users, as well as the owner, contributes their own findings. You can subscribe to an RSS feed of the forum to keep a note of the updates for the different airports.

For the last couple of years I've been travelling with a water bottle to avoid using more plastic than necessary when travelling, and this site has been helpful in finding where to fill it in the departure lounges I've visited.