Wet Weather

Water resistant means the fabric sheds light rain for a while, usually via a finish that wears off over time. Waterproof means the garment is built to keep water out under sustained exposure, normally with a membrane or coating and taped or welded seams.

Seams are the tell. A waterproof outer with untaped seams will let water in at the shoulders and hood long before the fabric fails.

Usually condensation rather than a leak. A fully waterproof shell also stops sweat escaping, so working hard inside one leaves you damp from the inside.

That is what pit zips, back vents and breathable membranes are for. If your work is high-exertion, a breathable jacket you can vent will keep you drier overall than a heavier fully-sealed one.

If your site requires hi vis, then yes — your rain jacket becomes your outermost layer, so it is the garment that has to comply. A compliant shirt underneath a plain rain jacket does not meet the requirement.

Rain also usually means poor light, so day and night taped versions are worth choosing over daylight-only fluorescent in wet conditions.