TOPIC: Glasspar Seafair water tank?

So I know I've looked into this before but never really got an answer, but now I have photo evidence!
My port side helm panel on the "59 has a deck water fill port on it. And there is a wooden cleat along the bulkhead near the bottom of the helm. I've heard rumors of early Seafairs having potable water tanks behind the dash but never actually seen one. Then I found this picture and you can see, port side water fill, same location as mine, and just popping out under the edge of the dash is what looks to be a tank held in place by the same wood cleat.

Does anyone know what this was all about? Was there a spigot somewhere? I have a mind to put a custom tank back there for fresh water to supply my head so I don't need to use sea water with all it's shortfalls...bacteria and organisms stinking, forming cement in my pipes, etc...