I've always found the "water volume" to be confusing. Most people in the US (imperial) don't use/talk in water volume anyway. Not that the metric system inherently means you have to measure tank volume with water....
Since you're in Atlanta, just use imperial. PSI/Cubic Feet. When you get fills or rent tanks, that's what people will use to reference things. That is, unless you're traveling outside of the US and Caribbean areas (Caribbean also seems to use imperial).
I had a discussion on a similar topic recently in another thread. Personally, I'm not opposed to using metric, but I would use metric to measure the gas volume in the tank. not water volume. I don't want water in my tanks anyway.
Maybe someday, I'll find a need to measure my tanks in water volume. The few tech classes I've taken did not mention it. If you frequent scubaboard for a while you will find there are a few scuba "issues" that seem to be strongly favored on scubaboard but not in the real world. Or maybe they're just popular in other parts of the real world than the ones in which I live and dive.
It's because you're overthinking it (on purpose?). You're getting hung up on what you have perceived as the important aspect, the "water" part, when it's entirely material agnostic. An AL80 is 11 units big. It holds 2200 units when it's filled to what's marked on the side of the tank. You breathe 20 units per minute at the surface. An AL80 is actually 77 units, but only at what's stamped on the side of the tank. If it's different, then not only is it not the 80 units it's advertised to be, it's not even the 77 units that actually matches what's written on the tank. Easy, right?
If I give you 10 oranges and you eat one a minute, it's pretty damn easy. If I give you 13 oranges and you eat 0.4 oranges a minute, that's stupid. If I give you a basket and tell you it holds 10 flingdingers, and it's written on the side that it holds 10 flingdingers, that's easy. If I give you a basket and tell you it holds 10 flingdingers but only under one single set of circumstances and now the circumstances aren't what's written on the basket, now tell me how many flingdingers you have.
Using imperial volumetric measurements are effing stupid. If I can learn to dive in metric, despite a lifetime of using imperial measurements for design, engineering, and construction, there's clearly an advantage. You seem to think that the real world of technical diving favors imperial? That's absolutely not the case whatsoever. The vast vast majority of technical dives around the world are conducted in metric. In fact, the only minor crossover is Mexico, where everyone dives in metric except visiting cave divers and some US instructors who have moved south.
If you like using imperial, that's fine, but don't try and tell people it's superior in any way because you're hung up on semantics. That's just silly.
(tongue firmly in cheek, trying to point out that unfamiliar units are more confusing than familiar units, no matter what you normally use)
(IMNSHO, YMMV etc)
