505: Fresh Water System Mystery

We have valves at each water tank which is standard.  If you close both of them, no water goes into the system, and the freshwater pump runs because its starved of water.  Great.  That's how its supposed to be.

Now, the weirdness.  When we close the valve on only the starboard tank, and proceed to use the bow tank, our water level in the starboard tank goes down as well.  Not as much as the bow tank, but definitely is not staying at 100%.  How is this possible?  There is only one way for water to come out of the tank, and its through that valve that is closed.

I validated that the valves do close properly and is why the water pump runs dry if I close them both.

What am I missing?

That's odd. 

When the valve on my starboard tank is closed, the tank remains full as the forward tank is emptied. As expected. 

I have noticed that if I open the starboard tank valve, and close the forward tank valve, the water pump is starved. It appears on my boat that the starboard tank drains into the forward tank and then on to the fresh water pump. Not sure if your boat is set up the same way or whether it sheds light on your mystery. But I'd be curious if your water pump will be starved if the forward valve is closed and the starboard opened. 

The tank valve  is about 2" away from the tank, so no possible alternate connection.  

When I look at the diagram on the Hanse manual, it doesnt show a second water line between the two tanks.  I guess I would need to expose the WHOLE tank and look around it to see if there is another possible connection between the two that is not documented.   I havent seen such a thing yet when poking around in the water system.  I will check the tanks again and see.  

Interesting.  Where is the input to the forward tank from the starboard tank?  I am going to go look for that.  I am not seeing it on the diagram Hanse provides but it wouldn't surprise me if the diagram is wrong.