It must not be cooling water. There are several sets of piping systems for water on board.
Ballast water system, cooling water system, fire protection system, domestic water (water supply and sewage) system.
You see that the ship is sailing while sailing, and it may be that any of these systems (the possibility of a ballast water system is not large) is working.
The ballast water adjusts the distribution of the ship's center of gravity by driving the seawater or river into the corresponding ballast tank when the ship is navigating at no load, or the cargo is not stowed (possibly for the next port of loading). Thereby adjusting the balance of the ship, before and after draught.
In general, the inlet and outlet valves of the ballast water system are below the water surface (of course, the ballast water system can also be connected to other systems through the adjustment of the corresponding valve), so generally, the working state is not seen.
The cooling system is used to cool the engine on board. The cooling system is divided into an inner circulation and an outer circulation. The inner circulation is fresh water, which flows directly through the engine cylinder liner and the like to cool the engine. The outer circulation is sea water, and the high temperature inner circulation water is cooled by the heat exchanger.
The outer circulation may have a valve above the water surface, and the cooling water can be seen to be discharged.
In addition to the 1211 (difluoro-chlorobromomethane) fire extinguishing agent system, the most important application is the seawater fire fighting system, which is to pump seawater to extinguish fires (sometimes used for washing, flushing decks, etc.). It is all visible.
Finally, the living water system (divided into and launched), the water is fresh water, mainly from fresh water tanks, like drinking water, bath water, etc.
Sometimes the crew also wash the glass with fresh water to prevent sea salt particles from affecting the line of sight. The sewage is also the sewage system, which is generally discharged into the designated sewage collection. Some ships have separation systems that separate the sewage from the solid waste. After the sewage is purified to a certain extent, it reaches the discharge standard and is discharged into the sea.
