Indeed, the Wikipedia page on the Vortex Tube mentions it has been successfully used with water when input at high pressure.
http://en.wikipedia.org/wiki/Vortex_tube
In 1988 R.T.Balmer applied liquid water as the working medium. It was found that when the inlet pressure is high, for instance 20-50 bar, the heat energy separation process exists in incompressible (liquids) vortex flow as well.
I hadn't heard of this before, interesting stuff!
Re:The microhydro plant
by maxerickson on Thursday December 12, 2013 @03:20PM
(#6896914)
It's the heat pump, at ~5 minutes.
http://www.youtube.com/watch?v=ggzfqRTzJ9M