RV Water Systems

The water system on an RV is basically a smaller version of the infrastructure that supplies your house. Most people don't like to think about their water until it stops working; they just assume that you get water when you turn on the faucet, and when you flush the toilet it all magically disappears. Living in a camper will put you in closer contact with two of the best things humans have ever developed: clean water and efficient waste management.

Since most Class A motorhomes are “self-contained” - meaning they don't require any external hook-ups for short stays - they carry their own supply of water. Even the old slide-in pickup campers and pop-ups had a water tank and pump to supply the sink. The complicated part comes from where the water goes after you use it. Simple (old) campers commonly had a drain hose from the sink that you routed outside, letting the waste water drain onto the ground. That is frowned upon today, and is definitely not an option for toilets. The solution is a three-water system of tanks and piping that is put together like this:

Clean (Blue) Water
My motorhome has a 90 gallon clean water tank, mounted to the frame under the bed in the rear of the coach. Being careful with water will stretch that out to a couple of weeks' worth of water; if I can find an outside toilet and shower, it'll last for a month.

The tank has a 12VDC pump to supply potable water to the kitchen sink, bathroom sink, water heater, toilet, and shower. The pump draws its power from the coach batteries (I covered the electrical system last week) and pumps around 3-4 gallons per minute, which is enough for a water-saving shower head or any faucet.

Standard RV water heaters are propane-fired versions of a household water heater that only hold 6 or 10 gallons, so you'll learn to take quick showers. Be sure to watch those water heaters carefully; the “instant on” point of use water heaters use a flow switch to start the heater, and if a faucet isn't open far enough to meet the minimum flow set point of the switch, there won't be any hot water.

There is a female garden hose fitting on the left (driver's) side, all the way to the back, for filling the tank. Most campers also have another female garden hose fitting for hooking into the water system at campgrounds or an outside faucet on a house. You'll want a pressure regulator on the garden hose (which needs to be rated for potable water) to prevent spikes in pressure, which can damage your plumbing -- campers water lines are made from plastic to allow some movement without breaking while you travel down the road, but they don't handle sudden pressure changes very well.

You also don't want to try to run the water pump and the campsite hookup at the same time! The campsite water pressure will be much higher than your pump can produce and it will force water backwards through your pump. This can lead to burned out pump motors, pump impellers coming off, or air getting trapped in your pump, all of which mean that your pump won't work when you need it.

Gray Water
Gray water is what goes down the drains from the shower and sinks. This water isn't clean, but since there is no human waste involved, but it's not quite sewage either. My gray water tank is broken pretty badly, so I'm going to have to replace it. The original tank was 60 gallons, and it sits between the frame rails of the chassis. There are a lot of pipes connected to the gray water tank and they're all glued in place. so it's going to be a pain to replace.

Watch what goes down your drains. Fats, oils, and grease (FOG in waste treatment terms) will coat the inside of your tank and block your level sensor. Once the layers get thick enough, they will blind off your drain port and prevent your tank from emptying. There are chemicals available to remove FOG, but they're mostly just a concentrated base like lye with some fragrance added.

Black Water
The waste from the toilet drops directly into the black water tank. That's the only direct connection, although some models will have an overflow from the gray water tank. Mine is supposed to have a 60 gallon black water tank, but I haven't measured it to make sure. With just the two of us using it, that should last at least a week before needing to dump it.

Since this is where the nasty stuff is stored, the black water tank will have a vent pipe that runs up the wall and vents above the roof. Mine has a 2 inch pipe and needs a new rain cap on the top - anything on the top of an RV is going to get exposed to a lot of weather as well as the wind from driving, so expect a lot of wear and tear up there.

Speaking of the sewage, I recommend using one of the biological treatments on the market to help digest the waste between dumpings. After a few days in warm weather, black water tanks get pretty rank as the waste ferments. I'll have a chance to test a few different brands next summer, but don't have a specific one to recommend right now.

RV toilets are odd in that they don't usually hold water until you get ready to use them; having a bowl full of water as you drive down the road is a good way to end up with wet floors. The normal procedure is:

1. Open the toilet lid. 
2. Step on the small lever to add water to the bowl, or on newer toilets push the single lever down part-way. Add as much as you think you'll need, usually about half-full. 
3. Use the toilet as normal, with the caveat that toilet paper for an RV is designed to break down (dissolve) quickly and isn't going to be as comfortable as household TP. 
4. To flush, step on the large lever, which also depresses the small lever (on newer toilets you just push the lever down all the way). The large lever opens the sliding gate allowing everything to drop into the black water tank, while the small one turns on water flow to flush everything down. 
5. When you're satisfied that the bowl is clear, close the lid. This isn't just to mollify the womenfolk; it will help keep bad odors from creeping back up and into your bathroom. 

Dumping Your Waste Tanks
Good campgrounds charge you a fee for overnight stays, mainly to pay for their infrastructure. Part of that infrastructure may be a sewer connection at each camper site, which means you can hook your drain hose up to a port in the ground and dump your tanks when they get about half full. This is great for extended stays, since it means you won't have to leave your camp site to find a place to dump the waste tanks. It's not a good idea to leave the dump valves open all the time because the solids will tend to stay in your tank unless you have a good supply of water moving to flush it out.

Several businesses have free dump stations as an incentive to get campers to stop at their stores; look for a Cabela's store or a Flying J truck stop. Interstate highway rest areas are another good place to find dump stations, and around here the county fair grounds usually have one as well. Other truck stops may have dump stations, but they may charge a small fee for their use. Joining one of the large campers groups will get you access to free dump stations at their locations as well.

How to dump your waste tanks:

1. Get the drain hose out of its storage compartment. That's usually the rear bumper, or at least near it. 
2. Connect the hose to your waste port. It's usually a 3" fitting with quarter-turn locking ears. 
3. Connect the other end of the hose to the dump station. A lot of times this is just sticking the tapered end of the hose into the hole in the ground, but some have locking tabs. Use the locks if they are available, as that will prevent smelly messes. 
4. Open the dump valves. There are differing opinions on the “correct” procedure, but the one that makes sense to me goes like this: 
1. If the black water tank is not full, open the cross-over valve from the gray water tank until it is at least 2/3 full. 
2. Close the cross-over valve and open the black water drain valve. 
3. Once the black water tank is empty, close the drain valve, open the cross-over valve again to flush it with the contents of the gray water tank. 
4. Drain both tanks and rinse both with fresh water. 
5. Adding a couple of gallons of water and your choice of treatment chemicals is a good last step. 
5. Flush the hose with clear water before putting it back in storage. 
6. Clean up any mess you may have made. The next person to use the dump station will appreciate it. 

I have heard tales of people in a bind having to dump their black water tanks into road ditches, and the scene from National Lampoon's Christmas Vacation of Cousin Eddie dumping his waste down a storm drain gets brought up whenever my friends hear about my purchase of an RV. I don't advise either method in civilized times (combined storm/sewer lines are a thing of the past), but if TSHTF, you'll dump waste where you can. Try to be somewhat considerate and at least cover your waste, though; insects and other pests will find it soon enough.


While my recent articles have been about the various parts of an older RV, most of the information is transferable to small cabins or off-grid houses as well; my small house just happens to be mobile.