How Do RV Water Systems Work?

RV water systems supply potable water to various fixtures – kitchen and bathroom sinks, toilets, indoor and outdoor showers, etc. In this article, we’ll focus on the design and function of your RV’s water distribution system and provide tips for using and maintaining it properly. 

How Do RV Water Systems Work?

Most RV water systems can operate as self-contained systems – meaning you draw from a tank of potable water on board. This tank is usually called your freshwater holding tank. This must be sanitized regularly to ensure safe water for drinking, dishes, and more. 

Potable: (adj.) safe to drink

Your RV water system pumps water throughout your coach using a water pump – a device that pressurizes the plumbing lines to drive water from the freshwater tank out through your faucets, fixtures, and hot water heater. The water heater must be turned on to heat water, which the pump distributes to hot water lines. 

Your RV water system also heats and distributes water to fixtures when connected to a city water source. A check valve in your water pump prevents your fresh water tank from filling when connected to city water. Another check valve at the city water inlet prevents water from flowing backward out of the inlet when the pump is running.

City water: (n.) a municipal water supply. In the case of RV parks, it can sometimes refer to water pulled from a local well and distributed via underground mains to campsite spigots. 

RV Water System RV Plumbing Diagram

Here’s a quick diagram of the basic design of RV water systems: 

Photo by Camping World

Disclaimer: This general diagram may not be 100% accurate for all RVs. Consult your owner’s manual or contact your RV manufacturer for an up-to-date diagram of your RV’s water system.

RV Water System Components

Here are the various components you’ll find in most RV water distribution systems:

Pressure Regulator

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Most RVs require the use of an external pressure regulator installed at the spigot if you’re connecting to city water. However, some units have a built-in regulator at the city water connection on the RV’s exterior wall. Most regulators also have backflow preventers and strainers to keep debris out of your RV’s water system. 

External and built-in models protect your water pump and system components from damage that can be caused by unregulated city water pressure. City water hookups can have pressures at high as 150 PSI (pounds per square inch). A pressure regulator reduces that pressure to an acceptable level for your RV – usually between 40 and 50 PSI. 

Learn more about why you need a water pressure regulator for your RV.

RV Water Filter Systems

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Some RVs are equipped with a water filter built into the distribution system. Others require installing an external water filter at the spigot (but after a pressure regulator, if applicable). 

Onboard filtration systems are typically installed in an underneath compartment or under the kitchen sink. They are usually cartridge-style filters that remove impurities that affect the incoming water’s texture and taste.

Onboard and external water filters must be replaced regularly according to the manufacturer’s recommendation. Water quality standards differ dramatically from region to region and campground to campground, so some water filtration mechanism is vital to safe RV adventures. 

Learn more about getting clean drinking water in your RV.  

Potable Water Tank (Fresh Water Tank)

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Potable water tanks are often made of polyethylene or a similar plastic material. The number of gallons of water these tanks hold depends on the make and model, as well as sometimes based on supply chain availability.

Most RVs have a permanent fresh water tank built into the RV in manufacturing, but some have a small, removable tank. Permanent RV potable water tanks are filled via a labeled fill port on most RVs’ off-camp side – opposite the main entry door.

In-line Strainer

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Most modern water pumps include a built-in strainer, but older RVs may have a separate in-line strainer installed between the water tank and the pump. These inline filters are simple screens that collect dirt, sand, and other debris before they can damage your water pump, check valves, vacuum breakers, and faucets. They do not filter the same impurities as a water filter.

Water Pump

RV water systems distribute water in three main ways: by a demand pressure system, a city water pressure system, or a manual pump system.

A demand pressure system utilizes a water pump powered by a small 12-volt motor. Most RV water pumps pressure to a range of 40-50 PSI. An internal pressure switch turns the pump off when the set pressure is reached. 

Most water pumps are also equipped with a strainer and check valve. The strainer removes large sediments that could damage the pump. The check valve prevents water from flowing backward through the pump into your potable water tank when connected to city water. 

A city water pressure system relies on the pressure supplied by a potable water source from a spigot. It requires a water pressure regulator to decrease pressure to a safe level for RV plumbing. 

A manual pump system utilizes a foot or hand-operated pump to pressurize the system and distribute water from the tank to the fixtures.  

Technician Tip: There was a fourth method for water distribution – air pressure. This method utilized an onboard air compressor to pressurize the system in place of a water pump. But it was more common on older RVs and is rarer to find now. Should you come across a pneumatic system, become fully trained in the use and maintenance of the system before use.

These systems will contain a very high volume of pressure, and severe injury can occur if extreme caution is not exercised. Also, the compressor must be food grade and likely oilless. Using the wrong compressor or maintaining it incorrectly can contaminate the potable water system.

Most RV fresh water distribution systems are designed to utilize two potential supply sources – demand pump (via your portable water tank) and city water are the most common.

Shut-Off Valve

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The shut-off valve in an RV water system keeps water in the tank if repairs are required in other parts of the distribution system. Closing the valve allows for repairs without draining the tank.

Piping/Tubing

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According to NFPA 1192, the piping that transports water from that tank to your fixtures must be rated for use with potable water. Pipes and tubes transporting hot water must also be rated for hot water use.

The most common piping material used in today’s RVs is CPVC or polyethylene cross-link tubing (PEX). Other common materials include PVC and polybutylene. The materials must be rated for hot and cold installations, and the requirements for material, type, size, installation, and support are all outlined in NFPA 1192. 

Water distribution piping is often red or blue but may be transparent or opaque. RVs with red and blue piping make identifying hot and cold water lines easier, but additional testing is required to determine if the lines are hot or cold for models with transparent or opaque piping.

Accumulator

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An accumulator tank is mostly found on higher-end units but can be added to any unit by a professional RV technician. It’s a small water storage tank (usually made of ABS plastic or metal) that’s located downstream from the water pump to help maintain consistent water pressure, reduce water sputtering, and minimize the cycling of the water pump. 

Internally, an accumulator is divided into two halves, separated by a rubber membrane. The user will pressurize half of the accumulator by adding compressed air through a Schrader valve, typically to 30 PSI. The water system will add pressurized water to the other half. 

When there is no demand on the system, the pressure is stored inside the tank and will be immediately released when a fixture or valve is opened. This provides immediate high-pressure water flow without delay. The water system then keeps the water flowing. 

If the water pump is being used, the accumulator will absorb the pulsations caused by the pumping action. This provides a smoother, more city-water-like experience. The air pressure is adjustable to fine-tune the performance to the user’s preference.

Water Heater

RV water heaters supply hot water to your fixtures and run on 120-volt AC power, propane, or both. Many RV water heaters today are known as DSI (direct spark ignition) water heaters. That means there’s no pilot light to be lit manually before each use. 

Water heaters that use propane must be listed for RV use because they must be designed and tested for the added vibrations and bouncing that come with the RV lifestyle. You’ll also see ‘on-demand’ or ‘tankless’ water heaters in many new RVs. 

Certain water heater installations may also include a bypass kit for easier winterization. This kit eliminates the need to fill the water heater with antifreeze to protect the tank and your hot water lines from freezing temperatures. Bypass kits can include 1-3 manual shut-off valves.

Technician Tip: Winterization shut-off valves should NOT be closed when winterizing a tankless, on-demand, or hydronic (boiler) water heater, as they MUST be protected from freezing by displacing all water with RV antifreeze.

Fixtures

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Most RVs are equipped with the following common fixtures: tubs, toilets, indoor and outdoor showers, and kitchen and bathroom sinks. These fixtures are the final element in your RV’s water distribution system before the water enters your RV’s plumbing system for waste collection. 

Approved RV fixtures must be listed and installed by the terms of that listing, such as those stipulated by the National Sanitary Foundation (NSF) and the International Association of Plumbing and Mechanical Officials (IAPMO). 

Low-Point Drains

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The low-point drains in an RV water system allow you to drain the system using gravity. However, the potential for low spots in the distribution system requires blowing out the lines using an air compressor or filling them with RV antifreeze when winterizing your RV.

Technician Tip: Due to the potential for freeze damage, there is no warranty at Camping World for the Basic Winterize Package (blowing lines out with compressed air). The Complete Winterize package includes blowing the lines out with compressed air and filling the lines with RV antifreeze, which carries Camping World’s standard warranty. 

Contact a Camping World Service Center to learn more about RV winterization services.

How to Maintain Your RV Water System

Now that you understand the basic operation of RV water systems, here are some tips to help you keep yours running smoothly and efficiently: 

Always use a pressure regulator and water filter when connecting to city water.  Always use a water filter when filling your fresh water tank from a potable water source.  Sanitize your fresh water tank before each use. Most RVers do this annually after dewinterizing their RV in the spring. Others do it every time their RV has sat without use for more than 2-4 weeks. Learn how to sanitize your fresh water tank.  Winterize your RV properly. Learn the basic steps for RV winterization in this tutorial.  Drain your water heater regularly and check the anode rod (for steel tanks). 

When you know how it functions, anything is easier to work on or troubleshoot. Hopefully, you now have a better understanding of RV water systems. Still, you can always contact an RV service advisor at your local Camping World Service Center if you need assistance. 

Do you have any questions about RV water systems? Let us know in the comments below.