Guide to watertightness of watches and clocks

The water-resistance of watches is a fundamental characteristic, as it allows us to use our timepieces in water sports activities. When it comes to determining the water-resistance of watches, various doubts arise, such as the differences between the different measurements that exist to evaluate their capacity, as well as the different tests and quality tests to which watches are subjected.

In this article, we will explain everything a watchmaking enthusiast needs to know about the water-resistance and watertightness of watches.

What is the watertightness of a watch?

Let’s start with the basics, by defining what this characteristic really is:

The water resistance of a watch is its ability to withstand exposure to water and pressure below the surface without compromising its functionality or aesthetics.

Although all watches are watertight as such, they are watertight to minor elements such as dust or air due to the way they are created. Whether a watch is water resistant, can come into contact with water, or is suitable for intense sporting activities such as diving, is determined by its degree of resistance, which is usually calculated in atmospheres.

Water resistance levels of watches

Water resistant watches are classified according to the level of pressure they can withstand before water enters the mechanism. These levels are especially important for users who are involved in water activities:

30 metres (3 ATM/3 Bar): This level of resistance is basically to withstand splashing water or rain. It is not suitable for swimming, diving, or any activity involving immersion in water.
50 metres (5 ATM/5 Bar): Good for for surface swimming and water sports but not for snorkelling or any activity at greater depths.
100 metres (10 ATM/10 Bar): Appropriate for swimming, snorkelling and other water activities but not for scuba diving.
200 metres (20 ATM/20 Bar): Suitable for recreational diving activities at moderate depths. Not suitable for technical diving at greater depths.
300 metres (30 ATM/30 Bar) and above: These watches are suitable for all forms of diving, including technical diving at great depths. They are preferred by professional divers and those who require a guarantee of endurance under extreme conditions.

Technology and materials that make watches water-resistant

Specific technologies and materials are used in the water-resistance of luxury watches to ensure that each watch can withstand the ingress of water under various conditions. These are some of the most common:

Screw-down crowns: This crown is screwed directly into the watch case, creating a watertight seal that prevents water from entering. It is essential in watches designed for diving.
Sealing gaskets: Gaskets, commonly made of materials such as rubber, neoprene or silicone, are used to seal critical points of the watch, including the crown, case and crystal.
Sapphire crystal: Used in most high-end watches because of its scratch resistance and clarity, sapphire crystal is also very effective in keeping the watch structure watertight. It is harder than mineral glass and much harder to break, making it ideal for sports and diving watches.
Titanium or stainless steel cases: These materials are not only highly resistant to saltwater corrosion, they are also durable and lightweight. Titanium, in particular, is highly valued in diving watches because of its hardness and light weight.
Helium valves: For deep diving, some watch cases are equipped with helium escape valves. During prolonged dives to great depths, helium can penetrate the watch due to its small molecular size. These valves allow the helium to escape during the ascent, thus avoiding internal pressure that could damage the watch.
Unidirectional rotating bezel: This type of bezel only rotates in one direction and helps divers track dive time safely, preventing it from accidentally moving in the wrong direction, which could result in a miscalculation of dive time.

These materials and technologies not only reflect the watch brands’ commitment to quality and functionality, but also ensure that the watches can be used in the most demanding conditions without compromising performance or durability.

Tests and industry standards

Luxury watch brands carry out extensive tests to ensure the water resistance of their watches, in accordance with international standards. One of the most common tests is the water resistance test, where the watch is immersed in water at different depths and pressures corresponding to its water resistance rating.

Another common test is the condensation test: the watch is heated and then rapidly cooled to see if condensation forms inside the crystal, which would indicate a seal failure. An air pressure test is also performed, where air is pumped into the closed watch to ensure that the case is completely watertight.

In terms of industry standards, the most prominent are ISO 22810 and ISO 6425. ISO 22810 sets out the minimum requirements for watches marketed as water resistant, including the tests and the conditions under which they must be performed. ISO 6425, specific to diving watches, sets more stringent criteria including visibility, water resistance and salt resistance. These standards ensure that watches are capable of handling everyday activities, but also more demanding underwater activities, allowing brands to promise reliability and durability in various aquatic conditions.

At Ideal jewellers we are distributors of the leading Swiss jewellery brands, with iconic diving watch collections such as Omega Seamaster or Longines Hydroconquest among many others. Discover them all in our online watch catalogue or visit us in our boutiques.