The water tank was delivered and temporarily hooked up because the plasterers need lots of water to do their stuff - they connect a garden hose to it and run the hose up into the house to wherever they're working. The tank is a fiberglass reservior that contains a pressurized bladder. When the water level gets low, the tank turns on the well pump and recharges itself. We opted for the big-size tank (this thing is over 6 feet tall), which not only provides more consistent water pressure, it also extends the life of the pump by not turning it on as often.