A waterproof watch does not exist. A watch can be rated for water-resistance, which means it has been tested to hold a water-tight seal for internal components to a certain depth, such as to 100 feet or 200 meters (660 feet). Water-resistant watches are designed to be more durable than other types of watches, and can be worn in the shower, while swimming or during a scuba dive, and continue to provide accurate time. Many watches operate on batteries, and replacing the batteries in water-resistant watches involves additional considerations to preserve internal components while immersed. Change the battery with caution.
Water-resistant watches have limited or strict warranties to ensure that this feature is preserved. Check your warranty and evaluate your usage because changing a watch battery yourself will most likely void the manufacturer's warranty. Consider local authorized service centers or reputable jewelers, who can replace the battery at a minimal cost while preserving the water-tight seal for the internal components. Consider whether you have the appropriate size of screwdriver, tweezers (or college pliers), silicone grease and replacement gasket (O ring), or if purchasing these items will save money and time.
Watches require at least one specialty battery, and some require two different specialty batteries. For example, the Casio Baby-G Force battery is water-resistant to at least 100 feet and uses CR1616 and CR2025 batteries, or a SR1120W (391) and a SR626SW battery. Check your user's manual or the manufacturer's website for specifications.
In many cases, the gasket or O ring can be cleaned and lubricated as part of a do-it-yourself replacement. However, carefully check the gasket using a magnifier to see whether there are any cracks, tears or irregular swelling in the O ring that may impair a water-tight seal. The O ring does not require special cleaning solvents, and can simply be wiped with a lint-free cloth before covering with a fine coating of silicone grease (make sure no fibers or hair attach to the slick gasket). If a gasket needs to be replaced, some manufacturers (such as Suunto) offer an O ring or battery package with a seal and replacement battery cover.
Water-resistant watches are pressure-tested to ensure that the seal is functional and that no air is released from the internal compartment at depth. This pressure test rates the level of water resistance for the watch. Most consumers do not have access to pressure-testing; some jewelers and all manufacturers include this test as part of the battery replacement service, which can involve additional waiting time.