The Hydrodisplacer works by interacting with Insta-Faucets and Insta-drains. If the Hydrodisplacer is empty, sticking it into an Insta-Faucet while standing on it's pad will cause it to automatically suck up the water it is connected to, and the faucet will turn into a drain. This water can then be poured into another source via an Insta-Drain. With this mechanic, the user can manipulate very large bodies of water to his advantage; for instance, he can drain all the water in a pool so that he can use the Heli-Pack to reach a higher ledge that he couldn't normally reach just be jumping out of the water. Most Hydrodisplacer puzzles are more complex than that, however. For instance, the user may have to drain a pool of water so that he can kill the Sewer Sharks so that he can cross safely, or so that he can open a door with the Trespasser before swimming through with the pool refilled.
- Originally, the Hydrodisplacer had a different design. Pre-release renders of the weapon showed that the tank the water was held in was in a seperate section on top of a main bar, making it appear like a water gun such as a Super Soaker. This design even showed up in the manual for the PAL version of the game.
- It's possible the Hydrodisplacer was invented by the Blarg as it was found on the BTS Station.