RE: Fiberglass tanks: It is extremely rare to find fiberglass fresh water tanks on any boat and if they are of any age cradle a vinyl bladder tank. They are expensive to fabricate, leach amines if epoxy, formaldehide if polyester and very hard to make leak proof. The vast majority on charter quality boats are food grade rotomolded polyethylene. Higher quality yachts use fabricated stainless.

That said, in high season the water in a charter boat tank does not have enough time to get "tanky", especially if you have newbies with long hair in the crew. <img src="http://www.traveltalkonline.com/forums/images/graemlins/jester.gif" alt="" />