The main water line, or service line, is the single pipe connecting a home’s plumbing system to the municipal water source or a private well. This line delivers all the clean water used inside the structure, supplying every fixture and appliance. Knowing the location of this line and its control points is crucial for managing the home’s water system. The ability to quickly stop the flow of water can mitigate significant damage during a plumbing emergency.
Locating the External Water Meter and Shutoff
The main water line starts at the property boundary, usually near the street or sidewalk. The water utility installs a water meter here to measure consumption, housed in a box buried flush with the ground. This external location is the first point of control, often containing a curb stop valve or access point to the main line shutoff.
The meter box lid is usually marked “Water” or “Meter” and is situated in the front yard or along the property line. The shutoff valve inside this box, called the curb stop, is primarily intended for utility use to perform maintenance or terminate service. Operating this valve often requires a specialized meter key, and in some jurisdictions, only utility personnel are legally allowed to use it. This external point divides responsibility: the line up to the meter is the utility’s concern, while the service line from the meter into the house is the homeowner’s responsibility.
Finding the Main Internal Shutoff Valve
The most relevant control point for the homeowner is the main internal shutoff valve, which is located where the service line first enters the physical structure. The exact location depends on the home’s foundation type and the local climate, particularly concerning freezing temperatures. When searching, find the thickest water pipe entering the home and follow it to the first valve installed on that line.
In homes with basements, the main water line typically enters through the front foundation wall, usually facing the street. The shutoff valve is generally located within three to five feet of this entry point, where the pipe emerges from the concrete floor or wall. For houses built on a crawl space, the valve might be located immediately inside a utility room or access panel above the crawl space.
Homes constructed on a concrete slab often have the internal shutoff valve in a utility area. Common locations include a utility closet near the water heater or furnace, or inside a laundry room. In some older slab homes, the valve may be found tucked away beneath the kitchen sink. The shutoff valve will appear as either a gate valve with a round, multi-turn wheel handle, or a modern ball valve with a lever handle.
Turning Off the Water Supply Safely
Operating the main internal shutoff valve correctly is necessary to prevent damage to the valve or the plumbing system. The method for turning off the water depends entirely on the type of valve installed.
Ball Valves
The ball valve is the newer and more reliable option, using a lever handle to control a rotating ball inside the pipe. To shut off the water, turn the lever handle a quarter-turn (90 degrees) until the handle is perpendicular to the direction of the pipe.
Gate Valves
The gate valve features a round wheel handle and controls water flow by raising or lowering a metal gate inside the pipe. To close a gate valve, the wheel must be turned fully clockwise for multiple rotations until it resists further movement. Caution is needed with older gate valves, as they are prone to corrosion and may seize or break if excessive force is applied.
After the valve is fully closed, open a faucet, such as a basement sink or an outdoor hose bib, to drain the remaining water. This step relieves any pressure trapped within the system.