My company is based in California, which is experiencing a terrible drought right now. We have a bunch of outdoor fountains, but facilities is concerned about turning them off because of possible damage to the concrete basin. Is this a valid concern? I would have thought water was more corrosive than air.
Carbon dioxide from the atmosphere can react with the calcium hydroxide in the concrete, effectively reversing calcification of lime in the concrete from the outer most surface inward. However if the water is left on then it would sow down by dilution of carbon dioxide into water. So I would say leave the water running unless its a major drought. The concrete is also probably tempered to withstand water better. I would check to make sure though.