RV Water System Explained: Fresh, Grey and Black Water
Understanding your RV water system is essential for any RVer. This guide covers fresh water tanks, grey water, black water tanks, and how to manage them all.
The RV water system is one of the first things new RVers need to understand. Unlike a house where everything happens invisibly in the walls, an RV requires you to actively manage your water supply and waste. Here's everything you need to know.
Fresh Water System
Your RV has a fresh water tank — typically 30-100 gallons depending on the size of your RV. This tank supplies all the water in your RV: sinks, shower, toilet, and outdoor shower if fitted. You fill the fresh water tank through a city water inlet on the exterior of your RV.
When connected to campsite water hookups you can also run water directly from the campsite supply without using your tank. Always use a water pressure regulator (set to 40-50 PSI) to protect your RV's plumbing from high municipal water pressure. A water filter inline with your city connection improves taste and removes contaminants.
Grey Water
Grey water is the wastewater from your sinks and shower. It drains to your grey water holding tank — typically 30-50 gallons. Grey water is relatively clean and in many areas can be legally dumped on the ground when boondocking away from water sources. Always check local regulations as rules vary by location.
Black Water
Black water is toilet waste. It goes into a separate black water holding tank — typically 20-40 gallons. Black water must be dumped at a proper dump station — never on the ground. Most campgrounds have dump stations, as do many truck stops, gas stations, and rest areas. The Sanidumps app is the best tool for finding dump stations.
Dumping Your Tanks
Always dump black water before grey water. The grey water flushes out the dump hose after the black water has emptied. Use a quality 20-foot sewer hose with good connections — a failed dump hose is one of the most unpleasant RV experiences possible. The Camco RhinoFLEX is the most popular and reliable option.
Tank Maintenance
Use enzyme-based tank treatments in your black tank after every dump. These break down waste and control odour. Never use formaldehyde-based treatments as they kill the beneficial bacteria and cause long-term problems. Keep the black tank valve closed when connected to sewer hookups — never leave it open as this causes a "poop pyramid" of solid waste that is extremely difficult to clear.