RV Water System Guide: Fresh, Grey, and Black Water Explained
Understanding your RV water system prevents the most common and unpleasant beginner mistakes. Here is a complete guide to fresh water, grey water, and black water management.
The RV water system has three separate tanks and associated plumbing that must be understood and maintained correctly. Neglecting any part leads to unpleasant consequences ranging from bad smells to expensive repairs.
The Fresh Water System
The fresh water tank holds potable water for drinking, cooking, and bathing when not connected to a city water source. Tank sizes range from 20-100 gallons depending on RV size. Connect to city water at campgrounds using a pressure regulator (to protect RV plumbing from high campground water pressure) and a water filter. Use NSF-rated potable water hoses — never garden hoses which leach chemicals into your drinking water.
The Grey Water Tank
Grey water is wastewater from sinks and showers — not the toilet. Grey tanks fill faster than most people expect. At a campsite with full hookups, connect the grey tank drain directly to the sewer connection and leave it open. When boondocking, the grey tank requires dumping at a dump station when full — typically every 3-5 days for two people. Do not dump grey water on the ground — it is environmentally harmful and often illegal on public land.
The Black Water Tank
The black tank holds toilet waste and is the aspect of RV life that most intimidates newcomers. Use only RV-specific toilet paper that dissolves rapidly in water — never standard household toilet paper which causes clogs and sensor issues. Add a tank treatment product after every dump. Keep the black tank valve closed until dumping — never leave it open like the grey tank as this causes pyramid plug buildup. Dump when approximately two-thirds full.
Dumping Procedure
Always dump the black tank first, then the grey tank — using the grey water to rinse the sewer hose. Use disposable gloves every time. A clear sewer hose elbow shows when the flow has cleared. Rinse the black tank with the built-in tank flush valve if equipped. Coil and store the sewer hose separately from water hoses.