Water resistance can be a confusing concept. It is very important to understand what it is, how to maintain it, and what environments it does not apply to. The term ‘waterproof’ was discontinued in the late 1960s. The US FTC found it to be a misleading term and misrepresented the product – keeps water out under normal circumstances, not every circumstance.
Water resistant means to what extent the watch can get wet, or withstand the pressure exerted by a specific amount of water. The degree to which a watch is made, water resistant is indicated on either the case back or the watch face. The unit (ATM, Bar, M, or FT) refer to the rate of the pressure test. These numbers will tell the amount of pressure the watch is manufactured to withstand. It does NOT refer to depth although this is a common misperception. It is important to remember that water resistance is measured at a static or motionless state under cold conditions. It does not take into consideration that pressure increases with velocity (motion). When you are swimming you are adding pressure simply by moving the watch in water.
Think of a watch that indicates 30M of water resistance: Your pool is 10M deep so you should be safe right? Well, the force of your arm crashing down as you swim will exceed the static pressures the watch was rated for. You are likely exerting 100M worth of pressure on your watch. A person will not scuba dive to depths of 200M however, if one is scuba diving then a WR200M+ watch is recommended.Watches are made water resistant by gaskets or rubber rings that are used to seal openings around the crown, crystal and/or stem. Also, a crown and case back can screw down to seal out moisture.Tips for Maintaining Water Resistance:Water resistance is not permanent and must be maintained as the watch ages. Seals will breakdown over time naturally becoming dry and brittle. Repeated exposure to chlorine, salt water, or soaps will accelerate this aging process.
- Check seals every 2-3 yrs for occasional exposure, at least once per year if used regularly for diving
- Anytime the case back is opened the gaskets must be replaced properly (i.e. battery changes)
- Always check that the crown is screwed in tightly if watch has a screw-down crown
General Guideline for WR levels:
- Do NOT wear water-resistant watches in a hot-shower, sauna or hot tub. Heat will distort the gaskets. Most watches are not pressurized for steam and condensation will form inside the watch with exposure to steam / heat. This causes rust to form in the movement and eventually it will not work.
- Water Resistant: Will resist moisture from accidental splashing, rain, sweat, etc.
- Water Resistant 30M: Will resist moisture and can be submerged, no swimming
- Water Resistant 50M: Will resist moisture and can also be worn while swimming in shallow water.
- Water Resistant 100M: Watch may be worn during snorkelling, skin-diving, and swimming.
- Water Resistant 200M+: Watch may be worn during standard scuba diving.
- Water Resistant 1000M: Watch may be worn for deep sea diving
Alternate depth designations other than meters (M) will likely be indicated as Feet or ATM's or Bars. 1 Bar = 1 Atmosphere (ATM)