Water-resistance markings such as 30 m, 100 m, or 200 m are among the most misunderstood specifications in watchmaking. The numbers themselves tell only part of the story. What truly matters is the ISO standard behind the rating—and how that standard should be interpreted in real-world use.

For modern, everyday watches, the relevant benchmark is ISO 22810. This standard defines how a watch may be labeled water resistant and the tests it must pass to support that claim. These tests simulate typical daily exposure to water, such as rain, hand washing, or, at higher ratings, light swimming. Crucially, the depth rating represents laboratory test pressure, not the depth at which the watch can be safely or repeatedly used. A watch marked “30 m” is therefore not suitable for swimming or diving.

An older standard, ISO 2281, served a similar purpose but has since been replaced. While it may still appear on vintage or discontinued models, it is no longer active and should be viewed as historical context rather than a current performance guarantee.

For scuba diving, a completely different and far stricter standard applies: ISO 6425. This is a safety-critical specification for true diver’s watches. It mandates a minimum water resistance of 100 meters, testing at 125% of the rated depth, legibility in total darkness, and functional safety features such as a unidirectional timing bezel and a running seconds indicator. Only watches that meet these requirements may legally be labeled “Diver’s Watch.” A high depth rating alone does not qualify.

Intended Use by ISO Standard

Are Vintage Watches Waterproof?

In most cases, vintage watches should not be considered waterproof, regardless of what may be printed on the dial or caseback.

Over time, seals and gaskets degrade. Rubber and synthetic materials harden, crack, or shrink, dramatically reducing their ability to keep moisture out. Many vintage watches were also produced before modern testing standards existed, or were evaluated using methods far less rigorous than those applied today.

Even when a vintage watch is pressure-tested, it is important to understand that a water-resistance test is only a snapshot in time. Passing a test confirms performance at that specific moment, under controlled conditions. It does not guarantee future resistance after temperature changes, shocks, crown operation, or normal wear. For older cases and components, the margin for failure can be very small.

For these reasons:

• Vintage watches should not be exposed to water
• Hand washing, rain, and humid environments should be avoided
• Any claimed water resistance should be supported by recent professional pressure testing, and even then treated cautiously

For collectors, vintage watches are best regarded as moisture-sensitive mechanical instruments, not modern tool watches. Preserving originality and movement condition is typically far more important than relying on water resistance that can never be guaranteed.

Final Takeaway

ISO 22810 defines water resistance for everyday life. ISO 6425 defines safety for diving. ISO 2281 belongs to the past. Understanding these distinctions—and the limits of testing—helps ensure a watch is used appropriately, safely, and in a way that preserves its longevity.