Originally Posted by Riverguy
Currently own both the Mainship and the Bayliner.
Anyway...Water's not the problem, it's the microbes that live off of the water and their corrosive bio-waste. Use a biocide, keep the bugs from growing, and sleep well at night.
Good point about warm and cold fuel, above and below ground storage, and the varying ability to hold water in suspension.
I disagree, water is a huge problem for metallic tanks, even if it's not supporting biological colonies. This is why, once again, I deem biocides a panacea, they address the symptom, not the cause. Water and no biological life is better than water and biological life, but water remains problematic, it shouldn't be dismissed as a mere nuisance.
Also, regarding water absorption by fuel in a tank, the inverse is also true, if the air in the tank is "dryer" than the fuel, i.e. it contains less water, water entrained in the fuel (not free water) will "evaporate" or be absorbed by the air.
Black contaminant in filters can be evidence of a microbial infestations (or more accurately its byproduct) or asphaltene contamination, the latter is mineral-based. Although some claim to clean tanks, no additive I've ever encountered will remove either of these per se, they need to be removed manually, by accessing and cleaning the tank.