What you're describing is Reverse Osmosis - pushing salt water through a water permeable, salt impermeable membrane. It requires very large pressures, on the or

What you're describing is Reverse Osmosis - pushing salt water through a water permeable, salt impermeable membrane. It requires very large pressures, on the order of 2-30 atmospheres of pressure. The membranes used are incredibly cheap, most of the cost of RO is the pumps and maintenance. IMO innovations on the membrane are pretty marginal to the cost of RO and are usually done for hype.