Hi Rudy: Our MT 44 is now 40 years of age. Teak decks and the fuel fittings go through the deck (teak and fiberglass) and sealed with black sealant. If there were a leak I would notice this on the pipe to the tanks. We have two 500 gal tanks original (black iron). We never had a leak and when we tested the tank there is no water. On our ocean cruising we kept the tanks full at our various stops. Now in fresh water and short distances we keep the tanks at 1/3 to 1/2 . When we winterize we add anti water protection and when we check the tanks next spring and summer there is no water. If we take on fuel that is done at busy marinas after I check out their fuel supply system before filling. Conclusion is any water would only come from the fuel supply as there is no way for water to get into the tanks otherwise. The above matches your conclusions. Leonard Stern, INDIFFERENCE