Water resistance in watchmaking refers to a watch's ability to withstand exposure to water without allowing it to penetrate the case and damage the internal components. This feature is crucial for maintaining the watch's functionality and longevity, especially for those used in aquatic environments or during activities involving water. Water resistance is typically measured in meters, atmospheres (ATM), or bars, indicating the depth or pressure the watch can endure. For instance, a watch rated at 30 meters is splash-resistant but not suitable for swimming, while a 100-meter rating indicates suitability for swimming and snorkeling.

Manufacturers achieve water resistance through various design elements, such as gaskets, screw-down crowns, and case backings, which create a seal to prevent water ingress. It's important to note that water resistance can diminish over time due to wear and tear, temperature changes, and aging of the sealing materials. Regular maintenance and testing are recommended to ensure the watch maintains its water-resistant properties. Additionally, water resistance ratings are tested under static conditions, meaning real-world activities involving movement and temperature fluctuations can affect the watch's performance. Therefore, users should adhere to the manufacturer's guidelines to preserve the watch's water resistance.