Silt can damage the pumps and membranes. Harbors and inland waterways tend to have much siltier, cloudier water than offshore. That cloudiness is the result of suspended solids, stirred up from the ocean floor, runoff from nearby homes, nitrates from fertilizers, algae blooms, and other large particulates that can plug up filters and work their way into your system. The large particles can damage feed pumps, score the pistons and cylinders of the high pressure pumps, damage valves, or even foul your membrane. Your watermaker will last longer between maintenance intervals if you operate your system when you are a few miles offshore, than if you try to operate it in a harbor or inland waterway.