Desalinating Drip-Irrigation System

http://www.patentstorm.us/patents/4698135/description.html

This patent is for a system that uses microporous hydrophobic materials such as Goretex to desalinate salt water within irrigation pipes that deliver the desalinated water directly to the root zones of plants.

I was thinking that something like this would be good to have and wondered if anyone had come up with a prototype. So I searched the Internet using the terms "desalination salt water irrigation," and found this patent application. Far as I know, this system is not being produced commercially. Based on the drawing that accompanies the patent application, the hydrophobic membranes are around the outer edges of the pipes.

My idea was to divide the pipe into two sections, separated by the membrane. Saltwater would flow along the bottom section of the pipe; water vapor would rise through the membrane and condense along the top of the pipe. The pipe would have small openings just above the membrane, to release the water to the soil. This would be simpler to make than the system described in the patent application, but there may be some reason this would not work well. For example, maybe the water has to be under pressure to keep the holes from clogging up with soil.