Can you post a picture of the complete assembly? I have the impression it is the pressure safety
When the cold water is heated is expands and the pressure increases. To prevent the tank from blowing up, the pressure relief valve “leaks” a small amount of water to bring the pressure down. On my boat
the outlet of the relief valve is to the outside of the hull
, but on other boats in can be to the bilge
So the “leaking“ of that valve only means it is doing its job.