What does water resistance actually work in watches and how will you know what your watch can withstand? Here are a few rating systems that will help to answer the questions above.
Water Resistance is a fairly common feature in most watches where you can see on your dial or caseback with a sign of ATM or BAR. ATM stands for atmospheric pressure and BAR stands for barometric pressure, after the device used to measure the same. The marking system on watches at 3 ATM/ 30m which is splash proof and waterproof in small amounts of water. 5ATM/ 50m can be submerged in water which is considered suitable for shallow swimming. 10ATM/100m is considered for swimming, snorkeling and water sports. Other than that more than 20 ATM and 30 ATM are usually for scuba and professional deep sea diving.
Water Resistance Chart

Now that you know all the ratings of the watch, don’t forget to check the mark stamped on a watch back that indicates how much water pressure can withstand.
Water Resistance: Do’s and Don’ts
Owning a watch can have different purposes in one’s life. One can use it for convenience and another for a statement piece. No matter what the purpose is, understanding your watch is important. Here’s the first one to start with.
DON’TS
Even though a water resistant watch can be worn in rain and shower and swimming (10ATM) , it is best to avoid doing so because chemicals from soaps can wear off on different watch components.
Even though 10 ATM water resistance may protect your watch while swimming, high impact on your watch during diving might have higher impact force and pressure than your watch’s resistance level.
Do not press the push or pull the crown when your watch is in contact with water.
Water and direct sunlight for long periods of time is the biggest enemy to any watch.
DO:After making sure to avoid the above-mentioned pitfalls, make sure you service your watch every once in a while, (1-2) years which ensures the gaskets are in working condition and can be replaced if they are.