Water proof or diver’s watches are the most top of the line when it comes to “swimability” and water safety. The crowns and buttons on these are typically all screw-down as well as the back to improve performance and safety. Gaskets on these usually are changed every time the battery is changed. often, the gaskets for the buttons and crowns are inside the cap, so many opt to change the whole crown when the time comes to change them. To best ensure your watch is at peak performance, make sure all buttons and crowns are completely screwed down before any contact with water. Also, if you notice scratches, chips or cracks in your crystal, make sure you have it replaced to make sure no errant drops find their way in through it.
Many avid watch collectors choose to have the water resistance of their watch tested every year or every few years to ensure that the seals are holding well. This can be done by sending it back to the manufacturer, taking it to a reputable jeweler with watch experience, or to a watchmaker.