Congratulations! You have a new watch on your wrist and the case back reads “Water Resistant 30 Meters.” Before you start taking a swim in your backyard pool or planning a diving adventure in the deep seas of the Caribbean, it is best to know that this watch is not intended for swimming and especially not for diving.
While it’s easy to assume that you can take your watch in water up to 30 meters or 100 feet, a watch with this designation is ideal for everyday use and can withstand casual exposure to water, such as splashes of water, being caught in the rain, accidentally wearing one in the shower or immersing into water.
Watchmakers today rely on the Water-Resistant standards created by the International Organization for Standardization in 1990, which use comprehensive laboratory tests to determine how well a watch is sealed against the entry of water.
The purpose of these tests is to determine the amount of pressure a watch can withstand while immersed in water and before water can force its way through the crystal seal, setting crown, and case back gasket. Temperature changes are also taken into consideration as well, since a watch may have to withstand both cold and hot water conditions.
The overall results from these tests are presented in units of pressure such as a Bar, Atmosphere or the equivalent of water depth in Meters or Feet. Hence, a watch water-resistant to 3 Bars or Atmospheres (ATM) can only withstand 30 overall meters of water exposure before condensation, erosion or any interference with the mechanisms inside start to taking place.
Watches with 50-meter water-resistance can be worn around household sinks and infrequent swimming in shallow water, however it’s best not to wear one when bathing, snorkeling or scuba diving.
100 meter water-resistant watches can withstand the same pressures as 50-meter models, yet you can also swim in deeper depths of water, dive or snorkel. However, it is best not to go deep-sea diving with one.
Timepieces with locking screw-down crowns, case backs and nylon, rubber or Teflon gaskets are expressly made for the rigors of deep-sea diving and are water-resistant up to 200 meters or more. Both screw-down crowns and case backs on these watches prevent water from entering the inner chambers of the timepiece, while the gaskets act as protective seals preventing water from entering the chambers.
Although a timepiece is labeled Water-Resistant it cannot be classified as Water Proof. The Federal Trade Commission prohibits watchmakers from using this claim even for deep-sea diving watches water-resistant, 200, 500, 1000 meters or more, since the seals that keep water out on these watches are not completely indestructible and their effectiveness may be reduced over any duration of time, taking both aging and deterioration into consideration.
Watch Water Resistance Guide
Here's a guide to help you determine how water resistant your watch really is: