Very good article of Bill Loyd in Watertechonline
Taking advantage of low pressure membranes in commercial systems
Note that AXEON Water Technologies has developped an extra low Energy RO membranes that are supposed to operate at pressure of 80 psi. I haven’t tried them yet, but this is an interesting innovation. Info here.
These types or membranes are very interesting for cold wheathers, where in winter, surface water drops to 5°C (41°F) and groundwater is between 7 and 10°C (45 -50°F) all year long.