Here's the real scoop: Water resistance of watches is rated based on a laboratory pressure tests comparable to a swimmer or diver sitting still at that pressure level. But many water-based activities involve a lot of movement and other environmental changes. These exceptions to how the watch was rated may challenge or defeat the water protection features of a water resistant watch.
In particular, the water resistance rating of a watch does not take in to account:
Even taking a shower or bath with your watch on can be bad for it. Besides the hot water issues already mentioned, many people do not realize that bath soap is a fine level abrasive. Soap can build up in the small, precision joints of the watch bracelet links. Over time this can wear down the link joints, ruining the bracelet. This is a greater issue with softer metals, such as gold. But steel can also be worn down this way too.
The term "waterproof" was discontinued starting in the late 1960's. This change was brought about from several government organizations, including the Federal Trade Commission in the USA, who were investigating truthfulness and accuracy of product labeling and advertising.
"Waterproof" was considered to have misrepresented the products as more capable of preventing the entry of water under normal use circumstances than they were actually capable of. Specifically, diving-type watches never have been completely 'proof' of water entry under normal use and within the stated depth ratings. The seals that keep water out are not completely impervious and their effectiveness can be reduced over time with age, deterioration, and exposure to chemicals.
The term "water resistant" is now used to describe such watches. There are no technical differences between a waterproof watch and a water resistant watch--they use the exact same methods and technologies to keep water out. The difference is only in what term was considered to appropriate to describe it at the time it was made.
The purpose and function of the helium relief valve is a common point of confusion. It has nothing to do with normal underwater diving. Neither does it have anything to do with the depth rating for a diving watch. Helium does NOT seep into the watch while the watch is in water at any depth!
To put it simply, you can completely ignore a helium relief valve. This feature is not used in any way with any form of normal SCUBA diving or anything else that involves less than a multi-million dollar deep sea exploration project.
SCUBA diving activities normally occur at depths of no more than 120 feet. At 250 feet, air becomes toxic due to changes caused by the high pressures at such depths. For those who do very deep sea research, they often use diving bells, dry dive suits, and other types of very deep ocean exploration vessels. In some of these, a highly helium-saturated atmosphere is used to avoid the air toxicity effect.
The purpose of a helium release valve is for people who wear their watch inside the helium-saturated environment for an extended period. Because helium is the smallest atom, it will seep through the watch's seals under the high air (not water) pressures in this environment. If the watch stays in this environment for an extended time, helium will continue to seep in to the watch until the air pressure inside the watch (initially surface air pressure) equalizes to the air pressure in the environment.
This becomes a problem when the vessel is brought back up and depressurized. The helium which seeped into the watch over a couple of days, cannot seep out any faster. The excess pressure inside the watch needs a way to release faster than it seeped in. It is only in this situation that a watch needs a helium relief valve at all. If a relief valve was not on the watch, the excess pressure would likely escape by pushing the crystal out.
But, unless you are in this exact situation, you should never keep this valve open. While the watch is designed to maintain most of its waterproof abilities even when the valve open, it still serves no purpose and increases risk of damage to the watch to do so.
This feature is so exotic that it really exists mostly as a curiosity. It makes the watch look more interesting and have an unique feature that other watchmakers are unlikely to copy.
No. Manufacturers and authorized dealers provide little to no explanation of the suitability and limitations of these products in the range of environments that normal consumers are likely to want to use them in. This leads consumers to assume that the watch will perform in any water-related circumstance that does not exceed the stated depth rating.
Divers understand the operation of their equipment and check it out before entering the water. But many divers watch owners do not understand the operations and limitations of their watches before exposing them to water. Neither do they always remember to check that the crown and helium relief valves are properly screwed down--violating the watertight integrity of the watch.
Most diving chronographs are not designed to have the chronograph buttons used under water. Doing so may let water in and ruin the watch. An exception to this is the Seamaster Professional Chronograph 300M, which is the first diving watch to used advanced seals around the chronograph buttons that allow all its functions to be used up to its rated depth.
Your diver's watch should give you years of enjoyment. To get the most of them, make sure you understand its correct operation and limitations so that you do not inadvertently abuse your watch.
Not a good idea for a number of reasons:
1. The water-resistant seals of a watch are far from permanent. With age, they dry out and lose their ability to keep water out of the watch. For using any water resistant watch in water activities, you should have it checked once a year to ensure its seals are still performing their job.
2. Any older water resistant watch should be able to be reconditioned, have new water seals installed, and tested. But considering the expense, you would be better off enjoying your older watch outside of the water and buying an inexpensive water resistant Seiko or Casio to use in the water.
3. Professional divers rely on their equipment. Under water, it can be a matter of life or death. Having an older watch fail or being mentally distracted if something damages your favorite vintage watch increases your risk of an underwater mistake that could impair your dive or risk your life.