Square Socket Wrench

Boiler Room: red toolbox on the floor inside the western fenced area. Powering the Boiler Room directly electrifies the water: plug the Elevator Passage instead (it opens Fuel Storage), shove the box aside, go through the hole in the fence and cross in the dark.

Unlocks the Collection Pool distributor panel and the north-west mesh cover in the Workshop (vent to the Service Passage).

The Technician's Note file hints at it. The same box holds an Empty Bottle; a Lockpick lies on the floor on the east side.