Basics of Boat Plumbing

Find out the basics about the plumbing on your boat

Someone in your neighborhood just bought a new boat. The boat is parked in their driveway, and you can’t overlook it. You run into your neighbor one day when leaving your house to go to work and you start making conversation. Your neighbor starts talking about all of the amazing times they have had with their family members out on the lake with the boat they own.

Skip forward a couple of months and you’re at the boat shop browsing around for a boat that fits your style. You’re smart enough to understand that you will need to do some more research before you dive deep and purchase a boat. What will your boat be used for? Should you buy a new boat without issues or take a chance and buy a used boat? Do you have enough storage space for a boat? What kind of boat will you get with your budget? What type of insurance will you need? A large thing that gets overlooked when purchasing a boat is the plumbing.

Water Reservoir Tanks

You will need some water reservoir tanks to be able to store water on your boat. Water reservoirs come in all sorts of different sizes and shapes. Because water can be very heavy, water reservoirs should be mounted as low as possible and balanced on your boat as much as possible.

Water reservoir tanks usually have three ports. Two 1/2" threaded ports, one for the outlet and the other for a vent. The third outlet is normally 1-1/2" and is used for filling the tank with clean, potable water. An on-deck fill cap is often used for filling the tank from the deck of the boat for convenience. The tank outlet should be connected to the on-deck fill cap with 1-1/2" food grade tubing.

The reason the tank is vented is to prevent the tank from imploding. Without a vent, a vacuum situation can be created by the water being pumped out of the tank. As the tank is pumped out and emptied it can implode. A vent allows air into the tank to equalize the pressure in the tank. The vent pipe should be piped to a point at least higher than the fill inlet, otherwise it will overflow when you are filling your water reservoir.

The outlet should be plumbed directly to your pump. We discuss different types of piping that can be used in the next section.

If you are installing hoses to the tank using barb fittings, be very careful not to overtighten the fittings. It is recommended to use marine grade stainless steel clamps to secure the hoses to the barb fittings.


It is required for all of the piping in your boat to be non-toxic and FDA approved for drinking water.

For many years, PVC piping reinforced with polyester braids have been the main choice for water supply piping. As of recent, cross-linked polyethylene (PEX) tubing has become the preferred choice. There are a few benefits of PEX tubing over PVC pipes. To begin, quick-connect fittings can be used and make installation and assembly much easier than ever before. PEX piping is avialalbe in red, blue and white all of which makes it harder for algae to grow within the tubing. If you use PEX pipe then you will want to use plastic fittings, like John Guest Speedfit quick connect fittings, or QickTite fittings, since marine conditions will corrode metal fittings. PEX tubing should not be used in locations exposed to sunlight.

Depending on what type of boat you buy, some boats will have either an electric or manual pump. Electrical pumps are used to pressurize the water system. Some electric pumps incorporate a pressure switch that will activate the pump when the pressure drops lower than the pre-set pressure value. They are usually set for 30-40 pounds per square inch (PSI), but are adjustable. Turning on a faucet releases pressure which causes the pump to turn on. The pump then runs until it rebuilds pressure to the pre-determined cut-out pressure setting. This pumping cycle will continue until the faucet is turned off. Some pumps can run dry and then automatically shut-off for protection to the pump.

The outlet of the tank gets plumbed to the inlet of the electrical pump and the pump outlet supplies water to your faucets.

Manual pumps are usually integrated into a single faucet that is plumbed to the outlet side of the tank. Water flow is controlled by rotating a handle back and forth which pumps water through the faucet and out through a spout. Although manual pumps are rarely the preferred choice, one great advantage they have is they waste far less water than electric pumps.

Drain hoses should be made of reinforced rubber. These types of hoses have at least three times the burst strength compared to regular clear vinyl hose. These reinforced rubber hoses are the same type of hoses used for radiator hoses on gas engines. When you are installing the drain hose, it is best to use double clamps to secure it.

Water Heaters

Water heaters are a great addition on a boat especially if your boat is big enough to have a shower. There are many different types of water heaters made for boats. Larger boats use tank sytle water heaters with electric heating elements and some also have a heat exchanger coil inside the water heater to circulate hot engine coolant through it to heat the water as the boat engine is operating. Smaller boats usually have a small capacity tank type water heater, although instantaneous water heaters are also available for marine use. Make sure the water heater is approved for marine use. It should be approved by The American Bureau of Shipping (ABS). Your water system must be pressurized in order to operate a water heater, as a pump will be needed to push water through the water heater and to your faucet.

Typical marine tank type water heaters contain four ports. A cold line teed off from the pump outlet should connect to the inlet of the water heater. The water heater outlet would then be piped to the hot sides of any faucets being used for hot water. Tee connections will be needed if more than one faucet needs hot water. The two other ports are used if you will be using the heat exchanger to run engine coolant through the coil inside the water heater. If you are planning on installing a water heater on your own, make sure to use stainless steel connectors, not plastic ones, to and from the water heater, due to the heat.

Faucets and Showers

The only differences between the faucets found in your home and the ones on your boat are styling and quality. Some boat manufacturers use less expensive faucets on boats to keep the costs down. Some buy specialty faucets that include barbed hot and cold inlet fittings for ease of installation.

Boat Drains

Boat drains are connected to a through-hull fitting via a reinforced rubber tube. It is a very good idea to run your drains into your toilet bowl. By doing this, you greatly reduce the risk of onboard flooding.

Although you may have the thought of emptying your shower into the bilge, it is not a very good idea. Bilge odors can become a problem over time, and the bilge pump can become clogged with hair. Shower pans should instead be separated from the bilge and have a discharge pump.

Marine Sanitation Systems

Federal law requires onboard toilets to have a marine sanitation device. Marine sanitation devices either reduce chloroform counts to levels that the human waste poses no hazard to public health, or store human waste until it can be discarded effectively onshore.

If you are in the ocean and more than three miles from the shoreline, it is completely legal to discharge untreated human waste overboard. If you are within three miles of the shoreline, it is illegal to discharge waste unless it has been treated with a marine sanitation device.

If you are operating your boat in non-navigable freshwater lakes or rivers it is illegal to discard any type of waste, treated or untreated.

In navigable freshwater, as long as the waste is treated, it can be discarded legally.

Final Thoughts

Owning a boat can be loads of fun. Whether you’re taking your family tubing on a lake during a hot summer day, or fishing off the coasts, spending time on your boat is something that will stick with you for the rest of your life. Owning a boat also comes with a lot of work and upkeep. A massive part of the equation is your boat’s plumbing. Luckily, most boat plumbing is easy to understand. If you make an effort to learn some basic plumbing skills, and know the regulations and laws, working on the plumbing for your boat is something that you can definitely do on your own.

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