The heads are connected through a system of pipes to the water mains or an alternative secure source of water. Most rooms require 1 or 2 sprinkler heads to afford complete protection.
The process of installation is similar to putting in central heating, but with much less pipework, and thus less disruption.
An adequate and reliable water supply is obviously essential for a sprinkler system. This can normally be obtained directly from the water mains, but in some cases may need to be stored on site.