i do not use fresh water on my topsides. i have glass over wood, most of this wood is teak, some still phillipine mahogany, but not much of that exists on here anymore--i wash my boat with buckets of salt water from under my boat--when i am cruising, i dont worry about the decking , as i dont want to fall on a slick deck. there is only a lot of dirt where boats are imprisoned--marinas, moorings, city anchorages
all have a lot of dirt coming into boats. boats dont care if the water washing
them is salt or fresh, unless there is teak wood involved in quantity--then should wash in salt, as fresh tends to rot
teakwood. i use oil
after my salt water dries, and only once per year, but then i have an older boat that looks so much better without that new boat shine.....