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Boat Plumbing 101: Understanding the Basics

Boat Plumbing 101: Understanding the Basics
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Boat plumbing is simpler than house plumbing, but if you’re new to boating or new to a boat with an on-board water system, then it may still be confusing (at first). Don’t worry – this guide will take you through the key components of your boat’s water system, their functions, and how they all work together.

Key Components of a Boat’s On-board Water System

There are typically seven components to a boat’s water system:

  1. Water reservoir tanks
  2. Piping
  3. Pumps
  4. Water heaters
  5. Faucets and showers
  6. Boat drains
  7. Marine sanitation systems

Water Reservoir Tanks

Water reservoirs, or water tanks, are used to store water on a boat. They come in a range of shapes and sizes, but because even a small amount of water can be heavy, they are always mounted low in the boat.

Water reservoir tanks will usually have three threaded ports:

  • One for the outlet
  • One for the vent hose
  • One for the fill hose

The outlet leads to a pump, manifold, or Y-valve depending on whether the boat has a single tank or multi-tank installation.

As water is sucked out of the tank, it creates a vacuum effect. This can cause the tank to implode as it becomes empty. The vent hose equalizes the pressure in the tank to keep it from imploding. This needs to be higher than the fill hose or it will overflow.

The fill hose is used to fill the tank with clean, potable water. For convenience, this may be connected to an on-deck fill cap using food-grade tubing.


The FDA requires all piping used to be non-toxic and approved for drinking water. The most preferred choice is cross-linked polyethylene (PEX) tubing. This tubing is available in opaque or semi translucent colors such as red, blue, and white to reduce algae growth.


Boats may have an electric or manual pump to keep the water system pressurized. Electric pumps are the preferred option, as they automatically run to rebuild pressure while a faucet is turned on. They may also have a pressure switch to activate when pressure drops below a pre-set value. The water reservoir tank’s outlet is plumbed into the electrical pump, and the faucets are supplied with water from the pump outlet.

Manual pumps use a rotating handle to pump the water through a single faucet. They are plumbed to the tank’s outlet side. Eco-conscious boaters may prefer manual pumps as they waste less water.

Water Heaters

Water heaters are insulated tanks most often used to heat water for showers. They are available in a range of types and sizes but typically use a heat exchanger and an electrical heating element. If you have a water heater, then you also need to have a pressurized water system for the pump to fill the water heater tank with water from the storage tank. Some may also use a heat exchanger coil to heat the water by circulating hot engine coolant while the boat engine is operating.

Water heaters may have up to four ports:

  • One to connect a cold line to the water heater’s inlet.
  • One to connect the outlet to the hot sides of any faucets.
  • Two for the heat exchanger.

Faucets and Showers

Boat faucets and showers are almost exactly like the ones used in homes, though they may look different. They will be used in sinks and showers to direct the flow of water. They will always have at least one connection for cold water, though some may have two for both a cold supply line and a hot supply line that connects to the water heater outlet.

Boat Drains

Once you pump water into your faucet, you need to be able to get it out of your boat. That’s where boat drains come in. These use reinforced rubber tubing to connect the drain to a through-hull fitting. The general recommendation is to run the drains to the toilet bowl to reduce the risk of on-board flooding. You should not empty the water in the bilge, as it can become clogged and develop an odor. Instead, you should have a discharge pump.

Marine Sanitation Systems

Marine sanitation systems ensure that human waste doesn’t pose a threat to public health. They are required by federal law and work by reducing chloroform counts or providing a way to store the waste until it can be properly discarded.

How to Maintain Your Boat’s Plumbing

To keep your boat’s plumbing in good working condition, you should inspect it regularly. This check can be added to your normal boat maintenance routine. You also want to keep all faucets, sinks, and showers clean to prevent buildup in the pipes and connections.

If you ever have questions about your boat’s plumbing or need help with maintenance or repair, never hesitate to contact a local professional! They will be happy to help you keep your boat in the best condition possible so it will last you for years to come.

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