Map of water taps to fill bottles
Openstreetmap with the cycle layer certainly shows some. Here's one
I was very grateful for in the French Alps.  OSM is not complete but it's open source so you can improve it (I haven't added any taps, but I have added bike parking).  This is a good approach, as it also shows cafes and shops where you should be able to buy water if there's no tap (flipping between the &quot;standard&quot; and &quot;cycling&quot; layers can show more facilities).
In the UK, the cafes on Cafe Network will almost all be very willing to fill bottles for customers - I normally plan on a cafe stop every few hours and take the opportunity then.  Pubs and coffee shops generally will too. Some chain fast food places won't - they say they can't. This is problematic late at night when nowhere else is open.
A possible fallback in the UK is churchyards - there's generally a tap outside, but no guarantee the pipes aren't lead.
It's possible to query OpenStreetMap for drinking water by modifying the following link to give an appropriate bounding box (the last 4 comma-separated numbers):
https://tools.wmflabs.org/query2map/featurelist.php?key=amenity&amp;value=drinking_water&amp;types=points-areas-infos&amp;BBOX=-2.9914,51.5871,-1.32,50.81
changing value=drinking_water to value=water_point returns some more (e.g. next to canals, for filling boat tanks).
Of course some are on private land.  I've seen campsites and schools showing all their water points.  But that's fairly obvious from zooming in.  The bigger downside is that many are missing.