How frequently do you use it? Do you drain the tank when you know it will be a while before you'll use it again? Do you let your boat set for weeks/months at a time? Our boat could go for months without us needing the freshwater system as we used it for day trips far more than overnighting. Again everyone is different.
When I lived in the Keys, I'd see probably a dozen "boaties" a year come into the hospital with some form of live-aboard mold/fungus issue. You get so many who fall for the romantic idea of "chucking it all and running away to the islands and living on a boat". Problem is they don't realize that when you live-aboard you become responsible for many hygienic things that you took for granted living in a house with a city water supply and septic system, not to mention the oppressive heat and humidity that makes boats living on the hook like Nature's own pitre dish!
I only drain it for the winter.
We use it everytime we take the boat out.
We wash up with it, shower with it, cook with it, sometimes drink it. We use it just like we do our house water.
I every so often fill it up right from the slip dock.
The kids love to run the water hose in the boat, they use the water more than us but for play time. So it is us 2 grandparents, our kids, their 3 kids typically using the boat.
Honestly, copper sterilizes water, google it.
Most of my water system is copper pipe and brass fittings.
Our boat water has never smelled or tasted bad.
http://www.investmentwatchblog.com/copper-kills-99-9-of-bacteria-within-two-hours/
Copper…plain old Copper kills viruses and bacteria on contact!!! Copper pipes and pennies too???
EPA registers copper-containing alloy products
On February 29, 2008, EPA registered five copper-containing alloy products. The registration allows the registrant, the Copper Development Association (CDA) to market these products with a claim that copper, when used in accordance with the label, “kills 99.9% of bacteria within two hours.” This Web page explains the conditions of the registration and provides information on the pesticidal claims.
www.epa.gov/pesticides/factsheets/copper-alloy-products.htm
I have noticed boats with plastic water systems, the water can be foul. Turn on the water on one for sale, and the stench was unbearable. And if the water system lets in any light, that's bad as algae will grow. I have seen a few boats with clearish opaque tubing.