Water Resistance
The water resistance figure on a dial is a laboratory pressure rating, not a real diving depth. 30 metres covers hand washing and rain, 50 metres covers showering and shallow swimming, and 100 metres is the ISO 6425 floor for a certified dive watch. No watch is truly waterproof; it is only water resistant.
Water resistance is measured under static pressure in a one-time lab test on a new watch, and the swimming you actually do adds only about 5 metres of equivalent dynamic pressure. The figure on the dial reads more optimistic than real life mainly because gaskets age and thermal cycling and impacts erode the seal over the years, not because of large dynamic loads.
What the ratings mean in practice
- 30 metres: hand washing and rain, not swimming
- 50 metres: showering, bathing, and shallow swimming
- 100 metres: swimming and snorkelling, and the ISO 6425 minimum for a certified diver's watch
- 200 metres and above: the recommended margin for scuba, though the formal dive watch floor is 100 metres
Gaskets perish over the years
Water resistance relies on the gaskets that seal the case, and those gaskets harden over time. If you really do swim or dive, periodic pressure testing is essential. Always check that a screw-down crown is fully closed before you get in the water.
For more, see the Water and Diving category and the Best Dive Watches Under $500 guide.
Related terms
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Frequently asked questions
Is 100 metres of water resistance enough for diving
Yes. 100 metres is the ISO 6425 minimum for a certified diver's watch, so it is enough for scuba alongside a screw-down crown, and 200 metres or more adds a recommended safety margin. 100 metres is also fine for everyday water contact and swimming.
Can I shower with a 30 metre water resistant watch
It is not advised. 30 metres survives hand washing and rain, but hot water vapour and soap stress the gaskets and raise the risk of a leak over time.
How do I keep the water resistance
Close the screw-down crown before water, have the gaskets pressure-tested every few years, and keep the watch out of hot water and saunas.