The standard sw30-2540 watermaker 2.5x40 membrane has been improved by
Dow and now rated at 700 gpd (29 gph) up from the old 540 ppd (22
gph). still same 800 psi.
http://www.dow.com/liquidseps/news/20030928a.htm

I'm researching building one (there was a good article in the Good Old
Boat mag Jan 2003 issue . Now I'm wondering about pumps and 120 vac hp
needed for the 700 rating as the higher permeate rating will reduce
the flow across the membrane and increase the clogging from the
reduced flow - dirty membranes being the biggest problem with under
sized raw water flow from small pumps and low hp.