sprinkler system

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A fire-extinguishing system consisting of a network of overhead pipes that release water automatically when a predetermined temperature has been reached.
• noun A system of underground pipes attached to sprinkler heads, used to water lawns.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a system for extinguishing fires; water from a network of overhead pipes is released through nozzles that open automatically with the rise in temperature