Apartment dwellers beware! Many of the tips for shutting off the main water supply to your residence may not apply. Before you're faced with a water emergency, consider the following. (Homeowners should follow along, too, because many of these tips also apply to you.)
Single-family residences (detached homes and most town homes and condominiums) almost always have two places to shut off all the water entering the home. One is at the water meter, and the other is a valve handle close to an exterior wall outside, in the basement, or near the water heater.
To save money in construction, apartments (especially older apartments) don't always have shut off valves for each individual dwelling unit. The latest building codes in most areas now require individual shut off valves to each unit to prevent the obvious disasters, but it wasn't always so.
If you pay your own individual water bill, then your unit probably has its own water meter (unless your apartment building prorates the overall water charges). If you have your own water meter, then you should be able to shut off the water at your meter, and you very likely also have a separate shut off valve outside the apartment, in the basement, or inside the unit, just like a single-family home.
Of course, even if your entire apartment building has only one meter, you could also shut off water to the entire building in an emergency if you know where the meter is.
Whether an apartment dweller or living in a detached home, don't take much comfort in just knowing where your water meter is. You should look inside the meter box and see what it takes to turn off the water. If you find a valve handle, then you know you can quickly shut off the water if you need to.
But some meter shut off valves don't have handles and require a special tool or a wrench to close the valve. If you don't have the proper tool handy, your place could fill with water before you could get it shut off at the meter. You're better advised to understand the other alternatives you have for stopping a flood.
For instance, if you don't have a main shut off valve outside or inside your unit, you still have numerous individual shut off valves for most of your plumbing fixtures. If somehow your sink faucet blows a gasket and starts spewing water all over the kitchen, don't bother running for the main shut off valve. Reach under the sink and turn off the hot or cold water supply line to the faucet.
The same applies to your bathroom sinks. Under each is a hot water and cold water shut off valve. Your toilet also has a shut off valve behind it on the left side. The washing machine also has valve handles behind it for turning off water. Even the water heater has a valve handle on the cold water pipe coming into the top of the heater to shut off water.
Dishwasher? It's typically connected to the water line under the sink and can be shut off by turning off the valves to the sink faucet.
Refrigerator ice maker? It may be connected to a fitting on the cold water shut off under your sink, in which case you can just turn off that valve to stop the water. Or it may be tapped directly into a pipe under the sink or near your washing machine, but it in that case it usually has its own small shut off valve very close to where it's tapped in.
The only fixture that doesn't have its own special shut off valve is the tub and shower. That's because for most purposes, the tub or shower valve is effectively the shut off.
Of course, if you have a leak somewhere behind any of these valves, shutting them off won't do any good. That's when you really need to know where the main shut off or water meter shut off is.
The bottom line is in an emergency, first go for the shut off valve for the particular fixture that's spewing. If that doesn't work, then go for the main shut off, even if you have to shut down water to the entire building. The sooner you stop the flood, the better for everyone.