Boat Builder Information

Installing A Freshwater Tank

Boat for water tank article

Installing a freshwater tank can be so nice to have on smaller boats for drinking, showering and cooking.

Tap into an onboard water source by installing a freshwater tank.

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, 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.

Water tank for boat

How much weight will the tank add to your boat?


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.

Pump and hose

No need to spend a lot of money on the pump and hose. 

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, 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.

Drain Hole

The tank does not have to fit exactly in the space chosen, as it will flex when you fill it with water.

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.

Water on hands

How will you use your new onboard water system?

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!