Whilst the public water supply in Rome is eminently drinkable, at least some of the sources
from which it's drawn contain fairly high levels of dissolved minerals.

I've tried to balance this pair of pictures, to show the amount of deposits that had
built up on the Turtles' fountain, in Piazza Mattei, in only 21 months.

On the left, very soon after its restoration (shot on 15th Feb 2010) - on the right, taken
in mid-November the following year.