I guess this (that I found at Lake Garda, Italy) is a public drinking fountain.
Do they use public water or a local well at this Lake Garda drinking fountain?
And, if I get the text on the plate correct, it should be quality checked and safe to drink.
But do people drink out of the likes of it at Lake Garda or do people just buy bottled water?
Text on the plate:
GARDA UNO Spa
CIVICO ACQUEDOTTO
PUNTO DI PRELIEVO
Controllo Qualitá
In this case, it seems that the water comes from the water mains, so it should be safe, and it seems that it is also checked at that point.
The non-drinkable water in nearby busy places (villages/towns) is well labelled ("Non potabile"), or just has a safety sign "Non controllata" (not checked). Note: sometimes that is just to incentivize people to go into the nearby bar.
The rest of the question is more tricky, when there is no sign (or the sign "has seen several wars", i.e. it is very old so probably outdated): it depends. Mainly we also drink from such fountains. On mountains/hills they may not come from water mains, nor be controlled, but usually it is safe: they existed to provide drinking water. I just may not use them after heavy rains, or in very dry periods; those are the times that contamination may happen (from livestock). I also avoid them if the water is not constantly flowing in remote areas (or in winter, when only a few people are using it), or if it is visually not nice (e.g. a very rusty faucet).
Often it is fine and also very good water. And on mountains you may notice a door on the hillside (or a small building) nearby: it is a chamber of the village aqueduct (e.g. to compensate pressure, and to flush extra water), so that means the water is good quality.
The general understanding (I don't know if it's a proper rule) is that water from public fountains is drinkable unless it's written that's not ("NON POTABILE"). Generally, the authorities put such a sign even on non-controlled waters to avoid troubles, though I've drunk from officially non-drinkable fountains and the water was just fine.
Water from main is periodically checked and thus safe to drink unless some exceptional event (floods, technical faults, etc.) occurs; in that case the authorities put some temporary sign. The sign you posted says that water is from main and checked, thus it is safe.
As for the customs of people, in Italy there is the habit to drink bottled water even when good-quality tap water is available, probably because it's generally cheap (and cold and sparkling).
