A home's plumbing consists of two systems: supply lines that bring pressurized fresh water in, and drain-waste-vent lines that carry wastewater out by gravity. Every fixture has a local shut-off valve (under sinks, behind toilets) and the entire home has a main shut-off, usually near the water meter. Knowing where these valves are and how to close them is the single most important plumbing skill — it stops water damage in seconds during a leak or pipe burst.
Walk through your home and physically locate every shut-off valve. Test each one by turning it off and verifying water flow stops. Note any valves that are corroded or hard to turn — these should be serviced before an emergency forces their use.
A home's plumbing performs two completely separate jobs, handled by two completely separate sets of pipes that never mix. Supply lines carry fresh water under pressure from the municipal main (or a well) to every fixture — sinks, showers, toilets, dishwashers, and washing machines. Drain-waste-vent (DWV) lines carry used water away by gravity: they are not pressurized, which is why they must slope consistently downhill and why a clog is a fundamentally different kind of problem than a burst supply pipe. Understanding which system is involved in any given problem immediately narrows down both the diagnosis and the fix.
The single most important plumbing skill is knowing where your shut-off valves are. Every fixture has its own: look under any sink for two small valves on the supply lines (one hot, one cold), behind each toilet for a single valve on the wall or floor, and near a washing machine for valves on the supply hoses. Turn them clockwise to close. The whole house has a main shut-off valve, usually located near the water meter — often outside at the street, in a basement, or in a utility closet. When water is actively spraying from a burst pipe or failed connection, the only thing standing between you and thousands of dollars of water damage is how quickly you can close the right valve. Walk through your home now and locate every one. Some valves in older homes haven't been turned in years and may be stiff or corroded — exercising them periodically keeps them operational when it counts.
The most common plumbing problems homeowners face are dripping faucets, running toilets, and slow or blocked drains — and all three have straightforward DIY solutions. A dripping faucet typically indicates a worn washer or cartridge inside the faucet body, replaceable with basic tools for a few dollars in parts. A running toilet usually means the flapper valve at the bottom of the tank isn't sealing properly, or the fill valve is set to overfill — both repairs cost less than $15. Slow drains usually have a buildup of hair, soap scum, or grease in the trap or the adjacent drain line, removable with a drain snake or plunger before resorting to chemical drain openers.
Understanding the trap — the U-shaped section of pipe under every sink and floor drain — explains both why drains occasionally smell and why clogs tend to form where they do. The trap holds a small amount of water at all times, creating a seal that blocks sewer gases from entering the home through the drain. If a fixture goes unused for weeks (a guest bathroom, a vacation home), that water evaporates and sewer odors enter — solved by running the fixture for a few seconds. The same curve that holds water also catches hair and debris, making the trap the first place to check for a clog. Most traps can be removed by hand or with basic pliers and cleared without any specialized knowledge — a reasonable first repair for someone new to home maintenance.
This is a foundational topic with no prerequisites.
No prerequisites — this is a starting point.