Water is essential not only to live, but to perform almost any task you do. How much water and what you use it for will determine how complex a system you will want to keep in your van.
There are three types of water systems used in RVs.
The Fresh Water system provides clean water for drinking, bathing, flushing the toilet, and anything else in the RV that requires it. A fresh water tank can be located anywhere in an RV, but is usually mounted underneath it or underneath a couch or cabinet inside a smaller trailer or cabover camper.
The water tank will have a hose connected to a fill hatch on the outside of the vehicle. This resembles the fuel door and filler cap on your car and allows you to fill the tank with a hose.
The fresh water system also has a water pump that pressurizes water from the tank throughout the pipes in the rig to all the water fixtures in the van. These pumps will run on 12 volts DC from batteries. When a fixture (such as the kitchen faucet) is opened and water flows, the pressure in the system drops and this is detected by the pump. The pump will then turn on, supplying water to the fixture until it closes and the pressure is restored. Some RVs also have an accumulator tank, which holds water at pressure to prevent the pump from turning on when only a little water is used. An accumulator tank will increase the lifespan of the pump.
RVs also have a city water connection. Usually located in the fill hatch, it allows you to hook up a hose directly into your RVs fresh water lines, so you don't use water from the tank.
When water goes down the drain in the sink or the shower, it then becomes gray water. Grey water goes into a separate holding tank that is (hopefully) as large as the fresh water tank and sits there until it can be dumped at an appropriate station. Chemical additives can be added to the tank to cut down on the odors produced in the tank.
Water from the fresh system that goes to the toilet in your RV is called black water. A black water tank holds all the waste and toilet paper that gets flushed down. These tanks also have chemical additives that not only cut down the smell but also break down human waste and toilet paper to make the system less prone to problems and clogging.
Excess freshwater can be dumped anywhere if needed, but gray and especially black water need to be disposed of properly. The black and gray tank connect to a dump valve underneath the rig. A portable hose runs from this valve to the dump station or sewer hookup allowing the tanks to be emptied safely.
Some smaller campers will use the same tank for black and gray water, and may not have a blackwater/toilet system at all.
Water for Vandwellers
Obviously, since a van doesn't have nearly enough room for all of these things, you need to think about what your needs are. How much water do you want to keep in your van? Do you want a sink? Do you want a shower? Will you need a toilet? Do you want running water?
At the bare minimum, you'll want a source of drinking water. You can keep a flat of bottled water in the van. You can also keep a five gallon water jug with a simple hand pump like you would find in the store.
A slightly more complex system that would work (and one that I have in my own van) would be two small portable tanks, a sink, and a hand pump. There's several options in the store, including the very pump I used and the water tanks in question.
What I love about my own setup is how versatile it is. The kitchen cabinet has the sink built into the countertop with the water tanks underneath. The hand pump pulled fresh water up from one tank and the sink drains into the second. When the gray water tank is full and the fresh water tank is empty, I can simply take them out from under the sink and dump/refill them. Here's two pics to show you what I mean:
I usually dump my gray water into a bush since all it contains is water from when I do my dishes, and the fresh water tank is easy to fill at any of the water vending stations that charge anywhere from 15 to 30 cents a gallon. If you go with the tanks I did, I would recommend filling the fresh water tank with five gallons instead of the six it holds. This way when the fresh water is empty, you still have a gallon in the gray water tank. Trust me, that is one tank you do NOT want to have overflow.
You'll notice that I said "hand pump" in the past tense because around a year into living in my van, I found a deal on a 12v water pump from JC Whitney. This is a simple 12 volt water pump that is actually designed to go into small water jugs. Click here to go to the pump.
For a size comparison, this pump is the thickness of an old 35mm film canister and a little taller. It's paired with the following type of faucet:
The black button is a 12 volt switch designed to turn on a small on-demand pump. This faucet is
usually paired with a pump for an actual RV water tank, but works beautifully with the one listed above. My faucet is very similar to this. This combo is so powerful I have to be careful that water doesn't spray out of the sink!
I don't have any experience or advice with larger systems simply because I find that 6 gallons of fresh water is more than enough for my needs and lasts for about a week or so. I empty and refill the tanks when I do my weekly trip to the laundromat along with the other simple tasks.
One of the largest decisions to make about the layout of your van and how you'll live in it regards going to the bathroom. Most weekend campervans will have a small portable toilet, although you may not have room for one or need it in your van.
"How do you go to the bathroom?" is the question I get asked most often regarding vandwelling and living, and not to many sites or vandwellers are comfortable with answering that question, but I will as it's a very important thing to think about if you're going to live in your van.
Personally, I'm always around the cities with 24 hour businesses, and you may want to use the travelers motto: Go when you can. If you use the bathroom when you have a chance to at a restaurant or store, very rarely will you run into an overnight situation where you need to use the bathroom. It's the same principle when taking long car trips with kids - when you stop, use the bathroom even if you don't need to.
I do not have a bathroom in my van simply because of the area I live in and my gym membership. For situations overnight when all you need to do is pee, if you're a male it's as simple as "point and shoot" into a bottle that you can throw out the next day.
For women, there's a similar solution that I have heard of working very well from several of my female vandwelling/backpacking friends. Some camping companies sell a product that's referred to as the Lady J that directs flow and allows women to use it standing up. A friend swears that this works great with the aforementioned bottle. I listed the one she has in the store.
If you're determined to have an actual toilet in your van, there are several different routes you can go from simple to more expensive and complex just like with the water system. The most basic system I've heard of involves using a bucket lined with a garbage bag filled with cat litter or sawdust, using one of these:
Since a bucket isn't going to be very handy, if you want to go one step further, use the bags and a portable hassock:
Finally, if you want to go all out, Coleman and Reliance both make portable flush toilets. These have two holding tanks - one for fresh water and another in the bottom for black water. They flush using a hand pump, and to empty them out you take the bottom tank into any restroom and can simply pour it down the toilet. I recommend this one if you plan to keep one in the van.
Don't forget to buy the chemical treatment for the flushable toilets and the toilet paper designed for them!