Watch Water Resistance (ATM) Explained
In brief: Water resistance (ATM) is a pressure rating used for watches, indicating how much static water pressure a timepiece can withstand in a laboratory. Measured in atmospheres (1 ATM equals 10 metres), this rating does not correspond to a literal diving depth but rather its ability to resist water ingress during activities like handwashing, swimming, or diving.
What is Water Resistance (ATM)?
Water resistance in watches is measured in units called atmospheres, abbreviated as ATM. One ATM is equivalent to the static pressure exerted by a 10-metre column of water. Therefore, a watch rated at 3 ATM is tested to withstand pressure equivalent to 30 metres of static water. It is a critical, yet often misunderstood, specification. The rating is achieved under perfect, static laboratory conditions, which do not account for the dynamic pressure changes that occur in real-world situations. For instance, the movement of your arm while swimming, or the force of water from a shower, creates a pressure far greater than the static depth would suggest. The concept of a purpose-built water-resistant watch was famously popularised by Rolex with their "Oyster" case in 1926, which used a hermetically sealed system to protect the movement. Today, this principle is refined and standardised across the industry, but the core idea remains: to protect the delicate internal mechanism from the damaging effects of moisture and pressure.
How Water Resistance (ATM) works
The water resistance of a watch is achieved through a system of precision-engineered seals and components. The primary defence consists of rubber, nylon, or Teflon gaskets, often referred to as O-rings. These are strategically placed at all points of potential water ingress: the case back, the crystal (the glass face), and the crown (the winder). For higher levels of water resistance (typically 10 ATM and above), a screw-down crown and a screw-down case back are essential. Unlike a standard push-pull crown, a screw-down crown threads securely into the case, creating a much more robust and reliable seal. The thickness and material of the case and crystal also contribute significantly. During manufacturing, watches are tested in pressurised water tanks to ensure they meet their designated ATM rating. This meticulous construction creates a protective barrier, safeguarding the intricate movement from humidity, dust, and water.
Key characteristics
When assessing a watch, its water resistance rating is usually indicated on the dial or engraved on the case back, for example, "Water Resistant 5 ATM" or "WR 50M". This marking is your primary guide to its capabilities. The durability of this resistance is not permanent; it relies entirely on the integrity of the internal gaskets, which can degrade over time due to exposure to chemicals, temperature fluctuations, and general wear. Therefore, regular maintenance is crucial. There is no specific ‘feel’ to a water-resistant watch, although models with higher ATM ratings often feel more substantial due to their robust case construction.
Comparison table
| Attribute | Standard Watch (5-10 ATM) | Diver's Watch (ISO 6425) | Dress Watch |
|---|---|---|---|
| Typical Rating | 50-100 metres (5-10 ATM) | 200+ metres (20 ATM+), ISO certified | 30 metres (3 ATM) or less |
| Best For | Everyday wear, swimming, showering | Professional diving, serious water sports | Formal events, office environments |
| Key Features | Gaskets, often a screw-down crown | Screw-down crown, unidirectional bezel, high luminosity | Slim profile, often a leather strap, minimalist design |
| Durability | Good protection against common water exposure | Excellent; built to withstand high pressure and impacts | Low; highly susceptible to water damage |
| Care | Regular pressure tests, seal replacement every 2-3 years | Annual pressure testing and professional servicing | Avoid all contact with moisture and liquids |
Who is Water Resistance (ATM) best for?
Understanding your lifestyle is key to choosing the right ATM rating. For the majority of wearers, a watch rated at 5 ATM (50 metres) is perfectly sufficient. It provides peace of mind against everyday encounters with water, such as rain, splashes from washing hands, and even a quick swim. If your activities regularly include surface water sports like snorkelling, sailing, or waterskiing, stepping up to a 10 ATM (100 metres) watch is a wise investment. For serious recreational or professional divers, only a dedicated Diver's watch, typically rated at 20 ATM (200 metres) and certified under ISO 6425 standards, will suffice. Conversely, for someone whose watch is primarily for formal or office wear, a 3 ATM rating is adequate protection against accidental splashes.
Care and longevity
Maintaining your watch's water resistance is crucial for its longevity. The gaskets that create the seal can degrade over time, especially when exposed to chemicals like perfume, chlorine, or soap, as well as extreme temperature changes. It is vital to avoid wearing your watch in a hot shower or sauna, as the heat can cause the seals to expand and contract, compromising their integrity. Always ensure the crown is fully pushed in or, for higher-rated watches, screwed down securely before any contact with water. We recommend having your watch's water resistance tested by a professional every 18-24 months, or whenever the battery is replaced. This service involves checking and, if necessary, replacing the gaskets to ensure the seal remains intact.
Common questions
Is Water Resistance (ATM) hypoallergenic?
The ATM rating itself is a measure of pressure resistance and has no connection to whether a watch is hypoallergenic. The potential for an allergic reaction is determined by the materials used in the watch case, case back, and strap. Metals like 316L stainless steel are widely used and considered hypoallergenic for most people, while titanium is an even safer option for those with sensitive skin. The ATM rating simply ensures these materials are sealed against water.
How do you clean a water-resistant watch?
For a watch rated 5 ATM or higher, cleaning is straightforward. First, ensure the crown is securely pushed in or screwed down. You can then rinse the watch head under lukewarm fresh water, which is especially important after exposure to saltwater or chlorine to prevent corrosion or build-up. Use a very soft brush, like a toothbrush, to gently clean any crevices. Finally, pat it dry thoroughly with a soft, lint-free cloth. Never use harsh soaps or chemical cleaners.
Is Water Resistance (ATM) worth the money?
Absolutely. A reliable water resistance rating is one of the most practical features a watch can have. It provides invaluable protection for the delicate movement inside, safeguarding your investment against everyday accidents that could otherwise lead to costly repairs. For a relatively small difference in price, upgrading from a splash-proof 3 ATM watch to a 5 or 10 ATM model offers significantly more versatility and peace of mind, allowing you to wear your watch confidently through almost all of life's daily activities.
Water Resistance (ATM) at OD's Jewellers
At OD's Jewellers, we understand the importance of matching a watch to your lifestyle. We offer a curated selection of timepieces from leading brands, with water resistance ratings suitable for every need, from elegant dress watches to robust sports models. Explore our full collection to find your perfect timepiece. View our watches.