In the past, the watch industry used a standard that basically said you shouldn't go swimming with a watch unless it has 100M water resistance or more.
Unified criteria for water-resistance
To ensure the homogeneity and clarity of the information provided to clients, Patek Philippe has decided
to introduce a new unified standard of water-resistance set at 30 meters for all watches certified as water-
resistant –having been tested in air and underwater by immersion at an overpressure of 3 bars
(corresponding to a depth of 30 m). This measure makes it possible to guarantee the same performance
level across all the models concerned and to provide perfectly comprehensible information as to the day-
to-day activities in which clients can engage while wearing their watch: washing their hands, showering,
bathing, swimming and other aquatic activities, including diving to a depth of 30 m – which corresponds
in large measure to actual utilization.