Basically, if the handle is turned 90 degrees to the flow, the valve is switched off. Contrastingly, if the handle remains in line with the flow path, it is on, and fully functional in alignment with your shower system.
Ball valves
Open or closed: When the handle of a ball valve is parallel to the valve or pipe, it's open. When it's perpendicular, it's closed. This makes it easy to know if a ball valve is open or closed, just by looking at it. The ball valve below is in the open position.
The master shutoff valve shuts off water to the house. Supply shutoff valves shut off the water to specific appliances and fixtures such as sinks, toilets, and washing machines. In most cases, the master shutoff valve to the home will have a wheel (gate valve) or a straight handle (ball valve).
Shut off the water by turning the ball valve 1/4 turn to make it perpendicular to the water pipe. If the ball valve is parallel, it is ON; if it is perpendicular (90° angle), it is OFF. The water meter should also be able to tell you if you have a plumbing leak somewhere in your home.
Locating the proper valve
Basements – the shut-off valve is typically located near the front foundation wall. The main water may come through the concrete floor or through the wall. The valve is typically within three to five feet of where the main water enters.
If your main valve is located inside your home, it can most likely be found in one of three places: your basement or crawlspace, your garage, or near your water heater. This is a small knob that is most likely labeled as your emergency shut off valve and probably red in color.
"There is no downside to turning off the water. It takes a little bit of time, and it can save thousands of dollars in potential water damage."
Just past the meter should be the main water shut-off valve, a red or green handle or knob. If you don't find the main water shut-off valve inside the house, check outside near an external faucet. This location is most common in warmer climates where frozen pipes aren't a concern.
While some buildings have the water meter inside the property, most modern homes have their shut-off valve outside. Here are some tips on how to find your main valve, and what to do to stop indoor flooding.
A clockwise rotation of the gate moves the stem back into the gate and closes the valve. When the stem is no longer protruding beyond the handle, the gate valve is closed. You can look at an OS&Y gate valve and tell if it is open or closed by the position of the stem.
The gate shutoff valve is round and shaped like a wheel. To close, turn the shut-off valve clockwise until it's firmly closed. The ball valve has a lever handle, and to close it, you turn the handle one-quarter clockwise until it's tightly closed.
A water shut-off is a primary control that turns off the water supply to your bathroom and kitchen plumbing. For example, it prevents flooding when you are planning to repair a fixture such as a faucet or toilet or when you are faced with a plumbing emergency, like a leak from a water heater or supply line.
Look for the oval-shaped valve knob. Sink valves are typically located just under the sink, toward the rear and near the bottom of the cabinet. Washer shut-off valves are typically just behind or above the washer, with one each for hot and cold supply lines.
Similar to gate valves, ball valves should be all the way open to allow the full flow of water or all the way closed to restrict all water from flowing. The valve is controlled by moving it between 0 and 90 degrees.
If you need to turn your water off for any reason, it's always safer to turn your water heater off, too. While many water heaters will be fine for a while without a water supply, reduced water pressure or a low water level inside the tank could cause the heater's components to overheat and burn.
Exterior faucets should have a separate shutoff valve inside the house, but not all of them do. In older homes, these valves are typically located at the ceiling somewhere close to the outside faucet. In newer homes, the valves are typically located right next to the main water valve, and they're also usually labeled.
Each individual fixture in your home—a sink, toilet, etc. —should have its own fixture shutoff valve that controls the water supply only to it. This allows you to do repairs or replacements without interrupting water flow to other areas.