This trophy is titled "
A Watery Grave" and it requires you to find seven Old Boilers hidden throughout the Regal Apartments.
Boiler 1) Once you're in the apartment building, after concluding your first investigation, walk straight ahead and toward the left wall. Pass through the door directly ahead that says Pool Room on the placard. You should see a shaking object directly ahead of you. Approach it and press R2, as prompted on-screen, to reveal the first boiler. Press Square to collect it.
Boiler 2) Turn to the right, pass through the pool table and through the wall with the people outlines to enter the Laundry Room. The boiler is against the wall you just passed through.
Boiler 3) Once entering the North Stairwell, turn to the left to find the boiler next to the stairs.
Boiler 4) Now on the 2nd floor of the Regal Apartments, enter into apartment 2A on the right side of the hall. The room will have three people playing poker. To the right of the tv will be a closet which contains the fourth boiler.
Boiler 5) Now on the 3rd floor, enter the apartment directly across from the stairwell. Exit the bedroom and enter the main room. In the back right, next to the refrigerator, is the fifth boiler.
Boiler 6) On the 4th floor, head down the hallway with the people and police. At the end, in the back left corner is the boiler.
Boiler 7) Turn around from boiler six and enter apartment 4A on the left. After the cutscene, head straight ahead into the bathroom to find the final boiler, unlocking the trophy.
Here is a YouTube video I used to find them all: