Water resistance ratings are precise about a specific test and silent about everything else. The gap between the test conditions and ordinary use is where most water damage occurs.
The rating describes a defined test
Ingress protection codes carry two digits, the first for solid particles and the second for liquids. The liquid digit corresponds to a particular procedure rather than to a general level of safety.
The higher liquid ratings involve immersion in fresh, still water at a stated depth for a stated duration, at temperatures close to the surrounding air.
Anything outside that procedure is untested rather than permitted. The rating is a statement about one experiment, not a description of what the device tolerates generally.
Pressure and movement are not in the test
Static immersion applies even pressure. Moving water, a jet from a tap or the force of diving into a pool produces localised pressure well above the equivalent depth.
Seals are designed against the tested condition, so pressures that exceed it can force water past a gasket that would have held indefinitely at rest.
This is why manufacturers advise against showers and swimming even on devices carrying strong immersion ratings. The difference is not caution alone; the conditions genuinely differ.
Water composition matters
Test procedures specify fresh water. Salt water is conductive and corrosive, and it leaves deposits as it dries that continue attacking contacts afterwards.
Soaps and detergents lower surface tension, which allows liquid to penetrate gaps that would repel plain water. Chlorinated pool water adds a further corrosive element.
Rinsing with clean water after exposure addresses the residue problem, though it obviously does nothing about liquid that has already entered.
Ratings apply to a new device
Adhesives and gaskets age, and every drop, flex and temperature cycle stresses them slightly. The seal that passed testing at manufacture is not the seal present two years later.
Repairs are a sharper break, since opening a device requires cutting the adhesive that forms the seal and the replacement rarely restores the original specification.
Warranty terms usually say so plainly
Liquid damage is commonly excluded from warranty coverage even on rated devices, and internal indicators that change colour on contact make it straightforward to identify.
This is consistent rather than contradictory: the rating describes expected performance under test conditions, while the warranty covers manufacturing defects.
Read together, the sensible interpretation is that a rating buys tolerance of accidents rather than permission for deliberate exposure.