How to Handle Water Leaks

Early this morning I had a call from a neighbor who receives my monthly newsletter. He had discovered water leaking in his hallway and onto the living room carpeting. We have inside water heaters, so the first question I asked was if the leak was coming from that area. When he said it wasn't, my next question was if he knew where the shutoff valve was located. He didn't, so I had him call the emergency number for our homeowners' association to have someone turn off the water in his unit right away. I also gave him the names of two reliable plumbers.
Mr Handyman recently wrote a column on how to handle leaks:

The most important thing is to know where to shut off the water, and to know this before you have an emergency.
Where are your on/off valves?
Per "appliance" valves - Every water "appliance" (faucet, toilet, water line to fridge ice maker, etc) has an on/off valve typically behind toilets and under sinks). These are called right angle stops.
Main valves - Single family homes, duplexes, four-plexes, etc, have a main water on/off valve that is generally near the house and on the outside of the house. It may be located inside a closet of some sort that in turn is open to the outside. Many sprinkler systems have main on/off valves for each yard.
If you live in a condominium or townhouse complex, the water valves could be anywhere. The HOA should have a map showing the locations of what valves turn the water off to what units. Generally water service within the complex is the responsibility of the HOA, rather than specific residences and/or the city.
City owned valves - For every property, there is a city owned and operated water valve. For single family homes it's under a concrete lid in the lawn or sidewalk. For HOA's, it could be anywhere but since it shuts off water the entire complex, it's not the one to use. You should never try to use the city owned valve to turn water off as if it's seized and it breaks, the city may charge you to replace it. At the bottom of this email are numbers for water services for all the cities in Santa Clara County. If you need them to come, call them. They tend to respond very quickly to emergencies.
After years of being open, valves can seize. When you have an emergency there is a tendency to force seized valves. When you have a fountain in your home it's hard to resist this urge, but you're better off moving to the next valve upstream. It will probably get the water off quicker.
For the record, there is a product named Liquid Wrench which loosens seized plumbing connections, including seized valves, and it really works. It's amazing stuff. Just follow the instructions on the can.
If you have an emergency leak in your home, try valves in the following order:
1) Right angle stop to specific device.
2) Main valve for house.
3) Call the city.
Sunnyvale - 408-730-7510
Santa Clara - 408-615-2000
San Jose - 408-279-7900
Cupertino - 408-279-7900