The water level is too high in the hatch. It blocks your way to the large metal door.
This is the low-spoiler guide for "Drain the water" puzzle in The Darkside Detective - A Fumble in the Dark. Unlike in normal walkthrough, you get gradual hints on how to solve the puzzle. Click the big button below to see your first hint. If the hint contains a spoiler, you will be warned about it before clicking.