a 55 Gallon Drum of Water — the weight

The liquid: 55 gallons of water is 459 lb. Add the drum — a steel tight-head runs 40–50 lb, poly about 22 lb — for a gross of roughly 480–510 lb. And if the drum is filled to the actual brim (a "55" really holds about 57.7 gallons), you're at ~530 lb gross.

Handling math follows: a standard 600 lb-rated drum dolly is fine; a hand truck rated 500 lb is marginal at brim-full; and rolling a full drum up a pickup ramp is a two-person-plus-winch job, not a favor to ask casually. Water's saving grace is that it's harmless when you give up and pump it instead.

Floor loading surprises people: 510 lb on a 23-inch-diameter footprint is fine on a slab and questionable on a cheap mezzanine. Check point-load ratings, not just area ratings, when storing drums up high.