Water resistance in a watch refers to the ability of a watch to resist the ingress of water. This is typically indicated by a rating system that is expressed in meters or feet (for example, "50 meters water-resistant" or "165 feet water-resistant"). The water-resistant rating of a watch is based on tests performed in laboratory conditions and can vary depending on the manufacturer.
It's important to understand that the water-resistant rating of a watch is not a guarantee that the watch will be completely impervious to water damage, but rather it provides an indication of the watch's ability to resist water under certain conditions.
For example, a watch that is rated 50 meters water-resistant can typically withstand splashes, rain, and brief immersion in shallow water, but should not be worn for activities like swimming or diving.
A 100-meter water-resistant rating for a watch means that it is designed to withstand water pressure equivalent to a depth of 100 meters (or 330 feet) in laboratory conditions. This rating is a standard measure of a watch's ability to resist water, and is often used to indicate that the watch is suitable for swimming and snorkeling, but not for diving.
The minimum water resistance recommended for a watch to be used for diving is typically around 200 meters (or 660 feet). This rating indicates that the watch is designed to withstand water pressure equivalent to a depth of 200 meters in laboratory conditions, making it suitable for scuba diving and other water activities.
In conclusion, keep in mind that the actual conditions in the water can affect a watch's ability to resist water, and the water resistance should be checked on a regular basis. Furthermore, the seals in a watch can wear down over time, compromising its water resistance. Different dive watch manufacturers may have slightly different standards and requirements for what qualifies as a dive watch, so it's best to seek professional advice or follow the specific recommendations for the watch in question.