The source of my confusion came from reading NAR, FAA, NFPA rules and trying to understand how they reconcile with WRA. Did this drive y'all nuts?
NAR:
Size. My model rocket will not weigh more than 1,500 grams (53 ounces)
at liftoff and will not contain more than 125 grams (4.4 ounces) of propellant or 320 N-sec (71.9 pound-seconds) of total impulse.
FAA:
(a) Class 1—Model Rocket means an amateur rocket that:
(1) Uses no more than 125 grams (4.4 ounces) of propellant; (ok that's specific)
(2) Uses a slow-burning propellant; (does this remove water rockets from Class 1 definition?)
(3) Is made of paper, wood, or breakable plastic; (does this mean they don't want us to use flexible plastic?)
(4) Contains no substantial metal parts; and (wow could they have used a more vague term?)
(5) Weighs no more than 1,500 grams (53 ounces), including the propellant. (I'm reading this as total liftoff weight)
NFPA:
Water powered, why would they care about water rockets? If we assume that the word propellant (which isn't defined by itself in the NFPA code) means a substance that produces thrust through combustion, water rockets have none. They define model rockets as having "model rocket motors" and model rocket motors must have "solid fuel propellant". Oh and mass launches now have to have expanded safety perimeters? Boy, every world record attempt for multiple launches sure violates that! They also want to discourage people from making "home built" rocket motors. Good thing water rockets don't have motors!
Again, I am following WRA rules regardless.