Can you scuba dive by using a garden hose?

Answer 1

No.

Years ago, when I took my very first Scuba course, the instructors had us walk from the shallow end of a pool to the deep end, wearing a weight belt and breathing through a very long snorkel. Nobody got all the way to the deep end before it became impossible to breathe against the increasing water pressure. It was a very effective exercise in that it taught us very quickly about the effects of ambient water pressure, which doubles in the first 33 feet of sea water.

If the intent of the question is to ask if one can breathe underwater through a garden hose used as a snorkel, the answer is "not deeper than a few feet". In fact, breathing through a snorkel deeper than about two feet is extraordinarily difficult. Your diaphragm simply isn't strong enough to displace the water at deeper depths.

One could use a hose like a garden hose with surface supplied air. The "snuba" systems used at some resorts use this approach. "Scuba", however, is defined as Self Contained Underwater Breathing Apparatus. It's a fair argument that any system which involves a surface gas supply is no longer "self contained".