Installing a Freshwater Tank
Tap into an onboard water source by installing a freshwater tank.
by Steve Noury
November 1, 2004
Most larger boats have some sort of built-in tank specifically for holding fresh water, which can
be nice for drinking, showering, cooking, etc. Smaller boats don't usually come with such an
option, but it's fairly easy to install one after the fact. Flexible tanks (usually made of some
sort of hard-but-flexible rubber) are the best option for this, as they can usually fit just about
anywhere on your boat where you might have a little extra room to spare.
Step 1
First, you'll want to consider weight distribution. A full 35-gallon water tank will add
considerable weight to your boat. If you plan to keep your tank full most of the time, find a spot
close to the center/middle of the boat. Most people probably won't fill the tank completely, except
on the occasional long-weekend cruise, so just about any place that's available will work. A
35.5-gallon Nauta Flexible Water Tank with fittings (FT911167, $220), marketed and sold by Imtra
Marine Products (www.imtra.com), is used in the example. This tank is installed on a 19-foot deck
boat in an under-the-seat storage locker near the stern of the boat. This particular location was
almost large enough to spread out. the entire tank, although it's not necessary for the space to be
the exact size of the tank (remember, it's flexible!).
Step 2
Most tanks come with the fittings/supplies that you need for a complete installation.
Purchase a small, inexpensive pump and a hose. If you're going to route the hose through the deck
or the sidewall of a seat, measure for the location of the hole where the hose will run. In this
example, a 2-1/2-inch hole is drilled into the sidewall. Add a T-connection to the pickup line on
the pump, and run one hose to the tank and the other to the water outside the boat, so you can use
either fresh water from the tank or raw water. After inserting the T-connection into the pickup
line, connect the hose from the tee to a shut-off valve. Then route and connect the hose from the
shut-off valve to the tank storage area hole that was drilled in the sidewall.
Step 3
Next, you need to cut (with scissors) a drain hole in the tank using the supplied rubber
gasket as a template. Don't cut it too large ' cut on the inside line of your template. The
manufacturer does not cut this hole because the tank can be installed in many different places on a
boat. Once the hole is cut, insert the supplied flange in the hole. It should be a tight fit, but
the flexible material will give. Next, put the copper gasket over the hole on the top side of the
flange, place the rubber gasket over the copper one, then place the brass ring on top of that with
the rib-side down. Place the locking ring on, and tighten everything down with the supplied spanor
wrench. Finally, install the elbow fitting into the drain hole.
Step 4
For this last step, place the tank in the selected location with the drain side down. The
tank does not have to fit exactly in the space chosen, as it will flex when you fill it with water
and conform for the best possible fit. Be sure that you have easy access to the fill hole on the
top of the tank. Connect the hose from the shut-off valve to the elbow fitting installed in the
drain hole. Last but not least, check all the connections, open the tank shut-off valve, and then
fill the tank with water and test the system for leaks and proper operation. If everything checks
out, you're ready to enjoy the luxury of fresh water no matter where you do your boating.