From the water heater, a pair of water lines-one hot and one cold-branch out through the house to serve the various fixtures (toilets, tubs, sinks, showers) and water-using appliances (dishwashers, washing machines, heating system boilers).

These supply lines are always under pressure; if they are opened or a break occurs, water will shoot out and not stop until it is shut off in some way. That is why modern homes have stop (or shutoff) valves for every fixture and appliance. If your home is not equipped with them, plan to install them. They'll make maintenance and repairs more convenient and will more than pay for themselves should you face a serious break.

Older homes have plumbing systems that use galvanized pipe, which will corrode over time, leading to low pressure and leaks. Newer homes use copper and plastic supply lines, which last much longer.