Plumbing Basics Every Homeowner Should Know

How Your Plumbing System Works

Your home plumbing system has two subsystems: the supply system that brings fresh water in under pressure, and the drain-waste-vent (DWV) system that carries wastewater out. The supply system uses pipes typically made of copper, PEX, or CPVC (older homes may have galvanized steel). The DWV system uses larger-diameter pipes made of PVC, ABS, or cast iron (in older homes) and relies on gravity rather than pressure.

The main water shut-off valve is the most important component to know the location of. This valve controls all water entering your house and is typically found near the water meter, in the basement, crawlspace, or on an exterior wall. In an emergency (burst pipe, major leak), shutting off this valve immediately minimizes water damage. Individual shut-off valves under sinks, behind toilets, and at appliances allow you to isolate specific fixtures without shutting off water to the entire house.

Common Pipe Materials

PEX (cross-linked polyethylene) has become the standard for new residential supply plumbing due to its flexibility, freeze resistance, and ease of installation. It requires fewer fittings than rigid pipe because it can bend around obstacles. Copper pipe is still widely used and offers excellent durability and heat resistance but is more expensive and requires soldering skills to install. CPVC is a rigid plastic alternative used primarily in warm-water applications.

For drain lines, PVC (white) and ABS (black) are the standard materials for residential use. Both are joined with solvent cement (glue) rather than solder. Cast iron was the standard for drain lines in homes built before the 1970s and is still used in some jurisdictions for main drain lines because of its durability and sound-dampening properties. Galvanized steel supply pipes, found in homes built before the 1960s, corrode from the inside over time and eventually become so restricted that water pressure drops to a trickle. If your home has galvanized pipes, plan for eventual replacement.

Preventing Frozen Pipes

Frozen pipes are one of the most common winter plumbing emergencies. When water freezes, it expands, which can split pipes and cause flooding when they thaw. Pipes most at risk are those on exterior walls, in unheated crawlspaces, and in unconditioned basements. Insulate exposed pipes with foam pipe insulation sleeves. During extreme cold, open cabinet doors under sinks to allow warm air to reach the pipes. Let faucets drip slightly to relieve pressure buildup from freezing water.

If a pipe freezes, open the faucet and apply gentle heat using a hair dryer, heat lamp, or heating pad. Never use an open flame. Work from the faucet back toward the frozen section. If you cannot locate the frozen section or if a pipe has burst, shut off the main water valve and call a plumber. Use our Pipe Volume Calculator to estimate how much water a pipe section holds.

Water Pressure Problems

Normal household water pressure is 40-80 PSI. Pressure below 40 PSI produces weak flow at fixtures. Pressure above 80 PSI can damage pipes, fixtures, and appliances. If you have low pressure throughout the house, the cause may be a partially closed main valve, clogged pipes, a failing pressure regulator, or corroded galvanized pipes. If low pressure affects only one fixture, the problem is usually a clogged aerator or valve at that fixture. Clean or replace the aerator first, as this is the most common cause of single-fixture low pressure.