Nearly every flagship carries an IP68 rating, which sounds like waterproofing and is something narrower.
What the numbers mean
The first digit is solid particle protection. Six is the maximum – dust-tight.
The second is liquid protection. Eight means immersion beyond one metre, with the depth and duration specified by the manufacturer rather than the standard.
So IP68 from two manufacturers can mean different things, and the details are in the small print.
What the test involves
Fresh water, still, at a specified depth and duration, on a new device at room temperature.
Not: salt water, chlorinated water, soapy water, pressurised water, hot water, or a phone that has been dropped.
Why ratings degrade
The seals are adhesive and rubber. Both age, both are affected by heat and impact, and neither is inspected. A two-year-old phone that has been dropped does not have the protection it left the factory with.
Repairs are the other factor. A screen replacement usually breaks the seal, and whether it is properly restored depends entirely on who did it.
Why water damage is not covered
Almost every manufacturer excludes liquid damage from warranty despite advertising the rating, on the grounds that the rating describes laboratory conditions and real exposure is not that.
Phones contain moisture indicators that change colour, and they are checked.
What to actually do
Treat the rating as protection against accidents rather than permission. Rinse with fresh water after salt or chlorine. Do not charge a wet phone – modern phones refuse, and that warning exists for a reason.