For the days it does not stop.

Water-resistant means a surface finish that sheds light rain for a while and then wets out. Waterproof means a membrane or coating that holds out sustained rain under pressure, and if it is certified it carries EN 343 with a class number. For a full day outdoors in Britain, water-resistant is not enough.

Two classes, each from 1 to 4. The first is resistance to water penetration — how waterproof it is. The second is water vapour resistance — how breathable it is. Both are printed by the pictogram. A cheap PVC suit is often top class on the first and bottom class on the second, which means dry from the outside and soaked from the inside.

If people are working hard in them, yes. A non-breathable suit traps sweat, so the wearer ends up wet anyway and cold the moment they stop — and in practice the suit gets left in the van. For short exposure, walking between buildings or standing at a gate, a cheap non-breathable suit is perfectly sensible.

Not where the hi-vis is required. Covering a certified hi-vis garment hides the certified material and defeats it, so the waterproof itself has to be certified to EN ISO 20471 at the class the site needs. That is a specific product, not an ordinary waterproof in a bright colour.

Wash it — which surprises people. A dirty outer face wets out and the garment feels like it has failed when the membrane is fine. Use a technical cleaner rather than detergent, never fabric softener, and reproof when water stops beading. Check the taped seams while it is off; lifting tape is usually what finishes a waterproof.

A size up from the normal garment size, because it is an outer layer, and two up if it goes over a fleece or a bodywarmer. A tight waterproof fails at the seams and restricts movement, and the slightly roomy one is the one people actually put on.