"Water pressure" is the term people use to describe the force of the water coming out of a shower head, a faucet, a hose, or any other plumbing device. What folks are really describing, however, is water flow. Water flow is the amount of water coming out of the fixture. Water pressure is measured when the system is closed – when all the fixtures are off.
High water flow makes for a great shower, quickly rinses the soap off your hands when you wash them, and blasts the food off your dishes. High water flow also lets you fill up your onboard tanks quickly.
The water flow to your boat is only as good as the narrowest point in your system. Most dockside hose connections have good water flow. But if you put a small in-line filter between that hookup and your boat, you will have disappointing water flow.
A full-size dual-canister dockside water filter system will give you great water flow, even while filtering, and even under heavy demand.