Differences in water resistance for luxury watches

Due to the rapid development of sports watches, water resistance has become so common that we often take it for granted. However, a closer look at this common feature reveals its intricacies.

How to make a watch water-resistant:

Several factors contribute to a watch's water resistance. The most important is the gasket, or O-ring, made of rubber, nylon, or Teflon. It creates a watertight seal at the joints between the crystal, case back, crown, and case. For chronographs, the pushers also have gaskets. Additionally, water-resistant cases are lined with sealing layers to prevent water ingress. The thickness and material of the case are also important factors in determining whether a watch can be safely worn underwater.

Using a screw-down case back instead of a press-fit one also aids water resistance. Many diving watches use a screw-down crown to prevent water from seeping through the winding stem hole. Tightening the crown creates a watertight seal, much like the seal between a jar and its screw-on lid.

Why not label it "fully waterproof":

According to guidelines issued by the US Federal Trade Commission, watch retailers cannot label their watches as "fully waterproof". Even if a watch is designed for deep-sea diving, it cannot be claimed to be fully waterproof.

What are the different levels of water resistance:

Watches with the lowest level of water resistance are only marked "water-resistant"; these can withstand splashes but should not be submerged. The next level, most commonly marked as water-resistant to 50 metres, indicates the watch is suitable for swimming; the next level is 100 metres, indicating suitability for snorkelling; followed by 200 metres, suitable for recreational diving with scuba gear; and further still to an incredible 1000 metres. Peter Purtschert, technical director at Breitling USA, points out that watches at this final level can be used for deep-sea diving, with gaskets made of materials resistant to helium in a diver's decompression chamber. Some watches are equipped with a valve that the wearer can use to release helium that has seeped into the watch, preventing the case from bursting when the watch and diver return to normal atmospheric pressure. The water resistance depth expressed in metres is only a theoretical value. It refers to the depth when both the watch and the water are completely still. This static condition does not exist in the real world for swimmers or divers. In real life, the movement of the wearer's arm in water significantly increases the water pressure on the watch, so it should not be worn to the theoretical depth indicated by laboratory testing machines.

In water resistance specifications, ATM stands for "atmosphere", which is equal to the pressure at a depth of 10 metres. Another term for atmospheric pressure is bar, often used in Europe.

Water resistance is not permanent and depends on several factors, some of which are affected by wear or time. Gaskets may corrode or deform, the case may be damaged, or the crystal may loosen or crack. Therefore, like your car and your teeth, a watch requires preventative maintenance and servicing.

How to test water resistance:

There are basically two machine-based methods for testing water resistance, known as "dry" and "wet" tests. In the dry test, air pressure is applied to the watch, and the case is measured for expansion due to air leakage. If it expands, the watch is not water-resistant. In one type of "wet" test, air pressure is first applied to the watch, and then it is submerged in water. If bubbles appear while the watch is underwater, it indicates that air had already seeped into the watch before immersion, meaning it is not water-resistant. Another "wet" test involves placing the watch in a small chamber filled with water and then pressurising it with a piston. If water enters the watch, it indicates the watch is not water-resistant.