What level of water resistance is necessary when washing your watch by hand? / Spring Q&A - Answering your watch questions

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2020.04.12

Q: What level of waterproofing is necessary when hand washing?

A: The most important measure to prevent COVID-19 (novel coronavirus infection) is to wash your hands and gargle. So, how waterproof is a mask to wear while washing your hands?

The Japan Clock & Watch Association divides the standards for waterproof watches into four categories: "Waterproof for saturation diving," "Waterproof for air diving," "Enhanced water resistance for everyday use," and "Waterproof for everyday use." Generally, only the first three categories are OK for hand washing.

Specifically, watches that are water resistant to 1000m, 600m, and 300m (saturation diving), 200m, 150m, and 100m (air diving), and 10 and 5 atmospheres (enhanced water resistance for everyday use) are suitable for hand washing. Watches that are generally water resistant to 30m (approximately 3 atmospheres) or 20m (approximately 2 atmospheres) are not suitable for hand washing. Note that watches that are water resistant to saturation diving and air diving, i.e., diver's watches, are required to be tested at 125% water pressure. In other words, diver's watches that advertise 100m water resistance have higher water resistance than watches that are water resistant to 10 atmospheres for everyday use. Also, since 10m water resistance is equivalent to 1 atmosphere, watches that are labeled as 10 atmospheres or 20 atmospheres water resistant, rather than 100m or 200m, can still be hand washed.

Seiko defines the usable range for each waterproof performance based on the JIS standard. 3 ATM water resistance (waterproof for everyday use) is considered to be "exposed to water such as washing your face or getting wet from rain." At first glance, it seems like it would be fine to wash your hands, but underneath it is the phrase "can be used without water pressure." When washing your hands, it is assumed that you will be exposed to water directly from the faucet, which means that water pressure will be applied, so it is clear that 3 ATM water resistance is insufficient.
Source: Seiko Watch Customer Service "Waterproofing (Maintenance)"

The relationship between water pressure and waterproof performance

So why is a water resistance of 5 atmospheres or more necessary when washing your hands? Holding your hands under running water creates a lot of pressure, which can allow water to get in through gaps in the crown and damage the watch. This is why even when doing simple housework, a high water resistance of 5 atmospheres (approximately 50 meters) is necessary. The standard for water resistance that allows a watch to be worn in situations where it will be submerged in water varies by manufacturer, with IWC requiring a minimum of 6 atmospheres.

Please note that these water resistance ratings are for new watches. The more a watch is used, the more the waterproof gaskets deteriorate, and the water resistance decreases. Even if a watch is labeled as being water resistant to 300m, it is safer to have it overhauled and the gaskets replaced if you plan to use it around water. If you buy a used watch that has not been serviced, it is probably best to avoid wearing it while washing your hands, no matter how water resistant it is.

What does 10 ATM water resistance mean? Explanation of water resistance and types of watches