While biking and wild camping around Mull and Colonsay this September I came across a system which was very helpful. A scheme, accessed via an app. that provides information of where you can refill your water bottles. This may be old news for some, but was new to me.
I think there may be other apps out there which perform the same function, but this one worked well for me:
https://www.citytosea.org.uk/campaign/refill/
I've always carried a Sawyer water filter while wild-camping to provide the freedom of getting water from a wide range of sources, and previously have also relied on calling into pubs and elsewhere to 'beg' for a refill etc. (although I believe that legally pubs are obliged to provide tap water on requested). Often, places in the scheme appear to have a designated tap, with the apps logo, situated outside, so the water is available even whether the building is closed.
Looking at the refill points on the app, many are B&Bs, hotels, YHAs, village halls and other community centres, and the like.