Question: Last week I was showing off my one-year-old boat to a friend and he noticed something I had not ever thought about before. The photo here is of the labeling on the potable water tank on my boat. It certainly indicates to me that the tank is fabricated from aluminum alloy. My friend says that aluminum is a really bad choice of materials to use for potable water tanks. I can’t believe my builder would use aluminum if it was such a bad choice. The boat does have the NMMA Certification using ABYC Standards sticker on it. So what’s up here?

Even though many aluminum water tanks carry certification placards, aluminum reacts poorly to chlorine over the long haul. Tanks made of 300-series stainless steel or FDA-approved plastic are far preferable.

Answer: An excellent question that raises several key points regarding standards compliance.

First, categorically the ABYC Standard that addresses potable water systems (ABYC H-23) recommends that aluminum not be used for potable water tanks. The standard talks about not using any materials for tank construction that might impart an undesirable taste, odor, or color to the water. The fact is that most tap water used here in the US today has to go through some form of chemical treatment to ensure that the water is safe to drink at all times. Unfortunately, one of the chemicals commonly used is chlorine, which can be corrosive to aluminum after long exposure. As the aluminum corrodes, it releases aluminum oxide, which turns into a white powder that frankly falls directly into the undesirable category when it comes to drinking water. I’m not an MD, so I can’t explain what the medical implications might be here, but I can tell you that the water in that tank will not taste too good after a while. Today the preferred choice for potable water tankage on boats is clearly centered around either FDA-approved plastics or 300-series stainless steel.

As for the reason your boat has an NMMA certification using ABYC Standards sticker on it, but does not comply with ABYC Standard H-23, it’s because that standard was not a part of the NMMA list of required compliance Standards at the time your boat was built. I just checked the NMMA required compliance standards checklist and found that H-23 is still not on the list. So, unfortunately your boat may still comply with the NMMA requirements and have an aluminum potable water tank. Unfortunately, these have been used extensively over the years. With what we know today, it's certainly not the best choice of materials.