Unlike most regular homes, which get their water via underground pipes or a well, RVs carry a supply of water for when they are not hooked up a city water system in a campground. The size of these tanks vaties from a couple of dozen gallons to a hundred gallons in large fifth wheels and motor coaches. When an RV is hooked up to an exterior water faucet, the water pressure on board will be the same as what is in the incoming line. But when the RV is on its own — not hooked up to an external water source — the water will be pumped from the onboard water storage tank to the sinks, shower and toilet by a 12-volt electrical water pump. These devices are hidden from view and only operate when a switch is flipped to activate them. Water faucets in RVs have both hot and cold running water. Most RVs have a six gallon hot water heater that is lit by flipping a switch inside the RV, usually on a control panel in the kitchen. A full tank of water will heat up in about 12 minutes, and will provide one shower (don't linger too long, however), before heating up again for another shower. RV waters are normally powered by propane. All but the smallest RVs come with a toilet, and most will also have a shower. Some will have a combination shower/bathtub. The toilet is a little different from the ones we have at home. It uses a pint of water a flush, which is important when an RVer is "boondocked" — in other words, camped without hookups. Showers, toilets and bathtubs use water from an onboard storage tank when the RV is not hooked up to a city water line in a campground. Taking a bath in such a circumstance would be unwise, because it would drain the tank. But many showers can be taken, each only taking a couple of gallons of water, even less with practice. Waste water from the bathroom as well as all sinks, goes into a holding tank, and can be emptied later at a waste dump station (available at some rest areas and public campgrounds, and most private RV parks). http://www.newrver.com/basic.html