What are the common misunderstandings about looking after a watch?

This answer is a draft. It stays unpublished until legal review and source verification are complete.

How to read the water-resistance marking on a wristwatch is one of the most misunderstood topics on Q&A sites in every country. Japan has its own industrial standard (JIS) that defines the water-resistance classes, and what "◯-bar water resistant" means is set out there. If you bought a watch in Japan, this is the system the label follows.

Water-resistance classes (a general summary based on JIS B7021)

"30 m water resistant" does not mean you can dive to 30 m. It is the value from a static pressure test; when you move your arm, the local pressure exceeds it.

[Verify] Check the classes and their intended uses against the Japan Clock & Watch Association's "About water resistance in watches" and the text of JIS B7021.

Misunderstanding 1｜A water-resistant watch is fine in the bath or an onsen

Changes in temperature make the gaskets expand and contract, and steam or soap can get inside. Many makers advise against wearing a watch while bathing or in a sauna.

Misunderstanding 2｜Water resistance lasts forever

What keeps water out is a rubber gasket, and rubber degrades with age. The usual advice is to have it replaced at battery changes or at a check-up every 2–3 years.

Misunderstanding 3｜If it gets wet, dry it with a hairdryer

Heat harms the inside of the watch. The basic rule: wipe with a dry, soft cloth, and if you see moisture inside the glass, take it to a watch shop promptly.

Misunderstanding 4｜Magnetism is an old-fashioned worry

Magnets in everyday objects are on the increase: smartphone and tablet covers, magnetic bag clasps, headphones. Both mechanical and quartz watches are affected, and magnetism can make them gain, lose or stop. The Japan Clock & Watch Association advises keeping watches at least 5 cm from magnetic products.

Misunderstanding 5｜No need to wipe off sweat

The salt in sweat causes rust and can cause metal allergy. Wiping the case back and strap with a dry cloth when you get home is a habit shared among people living in Japan.

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Sources

• Japan Clock & Watch Association, "About water resistance in watches" [一般社団法人日本時計協会「時計の防水について」]

https://www.jcwa.or.jp/etc/waterproof.html

• Japan Clock & Watch Association, "Watches and magnetism" [一般社団法人日本時計協会「時計と磁気」]

https://www.jcwa.or.jp/etc/magnetism.html

• Japanese Industrial Standards Committee (JISC), JIS B7021 "Water resistant watches" [日本産業標準調査会（JISC）JIS B7021「携帯時計の防水性能」]

https://www.jisc.go.jp/

⚠️ Editorial note: the source URLs above were identified by search. Our working environment cannot reach go.jp domains, so the contents have not been checked against the text. Verify every source before publication and record who checked it and when.

About this article

What we share here are ideas and everyday practices passed down among people living in Japan, together with general information drawn from public sources. They are not official recommendations, and they are not professional instruction. Practices vary between households and regions.

This is general information. Results vary from person to person and depend on your own conditions and surroundings.

Please decide for yourself, using your own judgement, whether any of this suits your situation. We cannot accept responsibility for any damage, loss or injury arising from following this article.

Follow the care label and the maker's instructions for any garment, shoe or bag. For expensive or sentimental items, ask a specialist cleaner or repairer.

Sources

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