would need to test the water to see how much iron and how many boats would be using. The tank I would reco would be 9" diameter x 48" high plus the manuel valve ( that means you have to clean it no electric to be concern with) and a brine tank (salt) 12x12 or larger if you want. I'll be taking my units home soon but if you want to stop by before and see let me know. Joe will be turning the water off soon. We could go smaller depending on the number of boat and how much you want to clean the unit (not to bad I usally clean the units when I'm chilling at the dock takes about an hour)