It's well-known that pipes rarely spring a leak during the normal working hours, when it's comparatively simple to get a plumber or the materials you need to make the repairs yourself. So it's a good idea to prepare for leaks before you hear the water running.
Two of the best emergency repair items to keep on hand are a pipe patch and an epoxy plumber's putty kit.
Pipe patches are simple clamp-on devices with rubber liners that you fasten over a leak in your pipe. Tighten the clamp with a screwdriver and your problem is over. If you shut off the water to the leaking pipe before you make the repair, you won't have a stream of water in your face while you work; but if for some reason you can't shut off the water, you can still apply the patch -- you'll just get wet.
That's not the case with epoxy putty. To use this stuff you have to shut off the water so the pipe's outer surface is dry and so the water pressure won't wash the putty away.
This putty usually comes in the form of two sticks. You break off equal sections and knead them together. Wear rubber gloves if you are allergic to epoxy, or put the putty in a plastic sandwich bag. Dry off the leaky area and press the putty onto the damaged area. Encircle the damage completely, and use enough to build up a strong wall around the leak. Then leave the water off until the putty has set up. This may take some time if the pipes are in a cold part of the house.
Since the pipe patch is quicker and doesn't require a water shutoff, it's your best bet whenever it can be used. You can't beat it for leaks in a run of straight pipe. But the patch won't do you any good if the leak comes at a joint in your plumbing system. That's when the putty takes over.
Epoxy putty is often sold at hardware stores, but if you can't find it there, go to a plumbing supply shop. You'll find it there for sure, along with pipe patches. Note that the patches are made in sizes to fit specific sizes of pipe. Be sure you get the right size or sizes to match the pipes in your house.
Okay, suppose a pipe springs a leak on a Sunday, or in the middle of the night, before you get a chance to stock up on these items. What then?
Often you can stop or at least slow down a leak by wrapping the pipe very tightly with layer after layer of plastic eletrician's tape. Cover the area of the leak and a few inches up the pipe in both directions.
Another trick is to cover the leak with a piece of rubber (inner tube or whatever you can find) and clamp it down with a hose clamp or two. If you don't have a clamp at home, you may be able to find an open gas station, although that's almost as hard as finding a plumber these days.