So do you put the membranes in parallel or series. Hint: Seawater has a salinity of about 35,000 ppm. Or 35,000 / 1,000,000 = .035 or 3.5% of seawater is not water. So even after you take out a lot of water from seawater, it still has a lot of water in it.

DIY Reverse Osmosis Watermaker – Part 4 – Parallel vs Series and Connecting all the Parts