Q Is the turf porous?
  A The backing material on our products is entirely porous. As a matter of fact, Tuff Turf Allsport has been tested to drain 37 inches of liquid per hour. This is more than enough to let even the most torential downpour simply drain right through.

Other companies cut holes in the backing of their turf to let the water flow through. One particular company here in Phoenix states on their website in the installation section that they "cut holes in the turf to let any water drain through".

Imagine the mold and mildew mess under turf that is not porous!