Just googled this answer and I found it helpful:
ATM or “atmospheres” is the amount of pressure a watch can withstand before leaking. A 3ATM watch will withstand pressures equivalent to about 30 meters, or 100ft under water. It is important to note that this is a measure of pressure NOT depth. For example, the pressure from the water coming from the shower hitting the seals of the watch is far greater than 3 atmospheres.
The following are “real world” examples of the water resistance of each rating:
3ATM - Water resistant to 30 meters (100 feet). Will withstand splashes of water or rain but should not be worn while swimming or diving.
5ATM - Water tested to 50 meters (165 feet). Suitable for showering or swimming in shallow water.
10ATM - Water tested to 100 meters (330 feet). Suitable for swimming and snorkeling.
so since this is 5 ATM, it suits my purposes and I'm buying one