I had a leak from somewhere under the port flooring that I unfortunately did not detect until a dark area on the ply manifested itself. The ply is in three pieces. Here two have been removed. This is looking forward and the bulkhead is forward of the water heater. The water heater is sitting on the third piece of ply. The forward salon top piece has also been removed and the fiberglass moulding loosened from the bulkhead.

See See the residue on the cold water inlet?

It was evident that the pressure relief valve had been weeping by way of the deposits on the cold water inlet. The ply under it was damp and partially delaminated. (Note: the pressure relief valve had been removed.)

See While youre at it...

..take the opportunity to rebed the screws holding the port belly water tank top in place. I had some weeping from the screws on the starboard side and had done it before. I had originally assumed the weeping was from this tank. I think they loosen over time with hull flexing, etc. (This is a 1994 model.) I dried everything and took a water-soluable white-board marker to outline the areas of apparent leaking and left it overnight to confirm where and where not the leaking originated. There was nothing at the water tank but was some by the hot water heater.

See One of the culprits

was this hot water heater pressure relief valve, removed and shown in the sink. Note: this is not a standard size. It is a 1/2 inch rather than the usual household heater 3/4 inch size. If it is bad, you will need to order one.

See Install an overflow hose to the relief valve

See the brass nipple added and the hose. I drilled a 1 hole in the ply piece directly under the heater (removed in this photo) so that discharge could go to the bilge. At this point I thought I was done