Not just residential irrigation, either. On a business trip to Phoenix some
ten or twelve years ago, I was appalled to see from the air all the swimming
pools, lush lawns, and heavily irrigated golf courses. Once on the ground and
headed to my meetings, what do I see in the plaza at the Phoenix civic center,
but this fountain:

http://tinyurl.com/38y86m

There might be a few fountains in the world that are more efficient at
evaporating water than that one, but not many, I'll wager. Especially in that
climate.

That's kind of the point. The fountain helps cool the plaza,
which would otherwise be even more of a giant stone solar oven.
This is classical roman technology, here.

Then, about my third day there, the local paper had a big article about a new
business that was coming to the area just north of Phoenix -- all excited
about the several hundred jobs it would provide. The business? A fish farm.

As long as it's a recirculating system, I don't see the problem.