Before water enters a preaction system, which must happen?

In a preaction sprinkler system, the correct sequence of operations requires that the detection system must be activated before water enters the system. This is a key characteristic of preaction systems, which are designed to provide an additional layer of protection against accidental discharge of water.

The purpose of the detection system is to identify a fire condition, which sends a signal to open the preaction valve and allow water to flow into the sprinkler pipes. This minimizes the risk of water damage that could occur from false alarms or unintended activation, as water does not enter the system until the detection system confirms a fire event has taken place.

The other options relate to various operational aspects of the system but do not address the critical requirement that the detection system must first be activated to permit water flow.