"Wayne.B" wrote
Perhaps Roger Long could cast some light on the question?

I struggled with this question a lot when international standards and
the Coast Guard's starting to enforce Public Health Department rules
made potable water skin tanks illegal in vessels. Watermakers have
eased the situation somewhat but I was designing sailing school
vessels before they were at the state of the art they are today.

Imagine putting enough water for a highly populated, slow, vessel that
makes long voyages into separate tanks with enough space to get around
the outsides for inspection and the bottoms two feet above any
possible bilge water level. You could use up 10% - 15% of the
vessel's usable accommodations capacity pretty easily.

The solution was to have a small potable water tank that went to the
galley and the drinking fountains and big skin tanks that went
everywhere else. All the other water outlets, such as in the heads,
would have a little sign that said, "Not suitable for drinking."
Everyone would brush their teeth or drink it anyway.

It's more of an issue on steel vessels where damage or a corrosion pin
hole wouldn't be discovered in the fresh water tanks. People might
get an unhealthy dose of salt without noticing it. Worse, they might
get some really nasty cholera bug in some port.

This isn't much different from our sailboat where the water in the big
tank tastes bad. Potable water is a bunch of plastic bottles under a
bunk. It's actually a lot easier to hand a new one up to the thirsty
helmsman than keep refilling a glass. Before any long voyages away
from reliable water supply though, I've got to tackle cleaning out
that tank and piping system.

When was the last time you found water seeping through a pin hole or
other damage in the skin of your fiberglass boat? That's about the
risk level of an integral tank. Without the Coast Guard looking over
my plans, I'd put an integral tank in any boat and just keep an eye on
the hull and the taste of the water.

Another reason though for using bottled water, despite confidence in
your tanks, is all the funky stuff that can get into marina hoses and
piping. It doesn't take much getting in when the pipes and hoses sit
out there warm in the sun. Even though we don't drink the water from
our tank, I like to fill it on a weekend when lots of people have been
hosing off their boats and filling their tanks just in case a guest
pours themselves a glass.

--

Roger Long