What "comfortable in water" actually means
For an SSI Basic Diver session: you need to be willing to put your face in water without flinching, exhale through a regulator while submerged, and stay calm when your buoyancy shifts. We test this in our 2-metre-deep pool before the open-water dive. Most people who *think* they can't swim actually can manage a few metres of paddling — the limit is comfort, not athletic ability. Children from age 8 can do Scuba Rangers (pool only) with similar requirements.
The Open Water swim test in detail
SSI and PADI both require the same minimum: a continuous 200 m swim using any stroke (no time limit) and 10 minutes of floating/treading water in deep water. No specific technique demanded — backstroke counts, doggy paddle counts. Or you can substitute a 300 m snorkel swim with mask, fins, and snorkel. Most people who do the swim test at our pool finish in 6-8 minutes; the float is the harder half for non-swimmers.