When I lived in Chicago the public water fountains just ran all the time. There was no button. The city is right on Lake Michigan so they have an abundant supply of fresh water. As I understand it, for many years they did not even meter water for residential service, you just paid a flat fee every month.
Unmetered water service is (or was) common in, of all places, California's Central Valley, including the cities of Sacramento, Bakersfield, Modesto, Merced, and Lodi, legacy of the state's rather arcane (and highly nonscientific and environmentally hostile) Spanish-based water rights laws. Unsurprisingly, when meters were installed, even where billing wasn't based on usage, massive wastage through broken infrastructure was rapidly discovered, an interesting example of "what isn't measured cannot be managed".
Water is metered now, but still extraordinarily cheap.
Most forever-on fountains in the city are that way not because the water is abundant but rather as a means to reduce the amount of lead consumed by users.
Each spring all fountains run continuously for about a month to flush the system from winter stagnation.
Our service is metered over on the other side of the lake (Grand Rapids, MI), but I can only remember a couple of times we've had to restrict water usage (odd-even sprinkling was the worst of it) in the almost 40 years I can remember. Lake Michigan is a hell of a reservoir.
