An RV water system provides the conveniences of home while accommodating the unique demands of mobile travel. Unlike a stationary residence, an RV must manage the entire water cycle internally. This self-contained approach involves a dedicated network of tanks and plumbing designed to acquire, store, pressurize, and dispose of all water used during a trip. The system is built for versatility, allowing travelers to utilize external sources or rely entirely on onboard reserves when camping remotely.
Accessing and Storing Fresh Water
The RV water system offers travelers two primary methods for obtaining a potable water supply. The first involves connecting to a municipal source, often called the city water connection, which allows the RV to draw water directly from the campground’s pressurized system. This connection bypasses the RV’s internal water pump because the external pressure delivers water directly to the fixtures. A pressure regulator should always be used to protect the RV’s internal plumbing from excessively high external pressures.
When travelers are not connected to a pressurized external source, they rely on the onboard Fresh Water Tank. This tank is filled using a dedicated inlet port, typically located on the side of the RV. Filling can occur through a gravity-fill port or through a pressurized connection that uses external water pressure to rapidly fill the reservoir. Specialized, non-toxic potable water hoses are necessary for both filling the tank and connecting to the city water inlet to prevent contamination.
The Fresh Water Tank serves as the main reservoir for “dry camping,” or boondocking, when no external hookups are available. The capacity of this tank varies widely between RV models, often ranging from 30 gallons in smaller units to over 100 gallons in larger motorhomes. The water stored here is accessed and pressurized by the RV’s internal pump, which is activated whenever a faucet is opened.
Pressurizing and Delivering Water
The movement of water through the RV’s plumbing network is managed either by external pressure or through the vehicle’s own 12-volt water pump. When the RV is connected to a city water source, the external pressure forces the water through the lines, much like in a residential home. However, when relying on the onboard Fresh Water Tank, the 12-volt pump automatically takes over the function of creating pressure within the system.
This diaphragm-style pump draws power from the RV’s house battery and activates only when a drop in system pressure is detected, such as when a shower or faucet is turned on. The pump rapidly cycles to maintain a consistent pressure, typically ranging from 40 to 55 psi, which is sufficient for comfortable use. Once all fixtures are closed and the desired pressure is reached, an internal pressure switch shuts the pump off until the next demand for water occurs.
A portion of this pressurized water is routed to the Water Heater before being distributed to the hot water fixtures. RV water heaters are designed for flexibility and can often heat water using either propane gas or an electric heating element, or sometimes both simultaneously for faster recovery. Propane operation is common for rapid heating and use while dry camping, while electric operation is preferred when connected to shore power to conserve gas.
The Water Heater is a simple tank that holds and warms the water, with capacities often around 6 to 10 gallons. A bypass valve system is installed to divert water away from the tank during winterization, preventing unnecessary filling. Hot and cold water lines typically utilize PEX tubing, which is flexible and resistant to temperature changes and cracking. These lines ensure durability against road vibrations and deliver water to all terminal points, including the kitchen sink, bathroom shower, and toilet flush valve.
Managing Waste Water
All water used inside the RV, once it has passed through a fixture, is routed into one of two dedicated holding tanks for storage before disposal. The Grey Water Tank collects runoff from the sinks and the shower, containing soap residue and small food particles. This tank typically fills faster than the other, as it handles the bulk of the daily washing and cleaning water.
The Black Water Tank is reserved exclusively for toilet waste and flush water, containing organic matter and specialized chemicals used for odor control and breakdown. Both tanks are equipped with internal sensor probes designed to provide an approximate reading of the tank’s fill level on an interior monitoring panel. Due to the nature of the waste and buildup on the tank walls, these sensors are notoriously inaccurate, often showing a fuller tank than is actually present.
When the tanks are full, the contents must be disposed of at a designated dump station using a specialized sewer hose that connects to the RV’s main outlet port. The dumping process involves opening a series of manual gate valves that control the flow from each tank into the hose. It is standard practice to open the Black Water Tank valve first to ensure the heaviest waste is cleared immediately.
Once the black tank is empty, the valve is closed, and the Grey Water Tank valve is then opened. The relatively cleaner grey water flushes the sewer hose of any remaining black tank residue, preparing the hose for disconnection. Many RVs are equipped with a tank flush system, which injects clean water into the black tank through a dedicated inlet to rinse the interior walls and further break down any remaining solids before the final closure of the valves.