So I’ve been given this advice when walking less frequented routes and I can tell you that it may be the worst advice I’ve received. First, many cemeteries have been paved over for ease of maintenance and no longer have water taps. Second, those that do seem to either have locked gates or remove the handle so folks like us can’t use the water at will. And finally, if you do find an unlocked cemetery with an accessible water tap, there is zero chance that they are regularly testing it for potability. Doesn’t mean it will kill you, but there remains the chance that the lines are old and not used for drinking water.
Now in America, we don’t routinely test all of our taps nor balk at water from untested yet obviously “normal” sources. However, our guts are used to our water while Spanish guts are used to Spanish water, so even though the water may be perfectly potable, it doesn’t mean that the native biome won’t upset your tummy for a bit.