If you want to filter water before you fill the tanks using 20 -10 micron filters that makes sense. I leave the charcoal filtration at the galley sink.
It's not practical to filter to 20 microns to fill the tanks. (If you have a 100 gallon tank that is going to require a very industrial grade setup to fill a water tank before lunch time. What is practical is to use a basic 2 stage filter like you might get a local Home Depot / Lowes. Connect your hose to it and filter out the really ugly stuff. You'll catch rust and sediments that occur in a lot of water supplies. You can use basic garden hose style fittings and the dock
pressure will easily drive the filter just as it would in your house. These filters are very cheap
and can filter 1000's of gallons of dock
water. Something like the Seagull Filter at the galley sink works better for small amounts of water that you might feel the need to have say 15 micron filtration. You would filter only what you were going to drink or cook with. That filtration is small enough to catch cysts that might be in the water.