Overflow ??

Hi, I just noticed today that I have a small amount of water flowing through what looks like an over flow/runoff pipe, situated on the drivers side, near the sill of the vehicle, between the waste hose tap and the fresh water drain off hose tap. The pipe is clear and about 6mm in diameter there is also another very similar pipe close by it. The fresh water and waste have been drained. Could it be something to do with the hot water cylinder? Although the van is not being used for  habitation at present. Any advice welcomed.
Symbol ES. 09. On a boxer.

Not familiar with your type of van but is your hab battery near the pipe as they normaly have a 6mm clear pipe on them to vent when on charge water should not be coming out of a battery vent pipe though.

Thanks, just pulled a few things apart. Yes there is a battery vent pipe, but on inspection this is not the pipe leaking fluid. The pipe that was leaking water looks to be a slightly larger one which does come from the hot water tank/heater. I haven't seen this happen before, especially as the water heater isn't being used at present.
We just took the van out for a run! As the water heater unit hasn't been drained perhaps it's due to the hot weather expanding the water in the tank !?