All cruise ships—and indeed all large vessels—collect a certain amount of water at the very bottom of the hull in an area known as the "bilge." This water, called "bilge water," is not there by design for stability, but rather as a byproduct of normal operations. It comes from various sources including condensation, small leaks in cooling systems, drainage from deck cleaning, and incidental sea spray. Because this water often mixes with oil, fuel, and other fluids from the engine room, it cannot simply be pumped overboard. Modern cruise ships use sophisticated oily water separators to treat this mixture, ensuring it meets strict environmental standards before any filtered water is discharged. In terms of stability, ships do intentionally carry water at the bottom, but it is stored in "ballast tanks" rather than just sitting in the bilge. Ballast water is used to adjust the ship's center of gravity, compensate for the weight of consumed fuel or food, and ensure the vessel remains stable in rough seas. This water is carefully managed and treated to prevent the cross-continental transfer of invasive marine species when the tanks are emptied.