Most of the time indicate on the watch, or on the back cover, how waterproof a watch is. This is shown in different ways.
It is indicated in atm. bar and meters.
There are therefore 5 different designations and 3 versions
3 bar, 3 atm, 30 meters. If this is on your watch your watch is not waterproof but water resistant. You can keep your watch on hand washing but it is not intended to immerse your hands. Swimming is also not possible
 5 bar, 5 atm, 50 meters. If this is on your watch your watch is waterproof and it is possible to immerse the watch, you can take a shower and swim with it. (no diving)
10 bar, 10 atm, 100 meters. If this is on your watch then it is possible to snorkel and dive from a diving board.
20 bar, 20 atm, 200 meters. If this is on your watch, recreational diving is possible, but not deeper than 40 meters.
100 bar, 100 atm, 1000 meters. These are watches to dive with deep sea.
N.B. For watches with a leather strap it is always better to avoid contact with water. This will significantly extend the life of the tire. In general, a leather strap lasts about one year to one and a half years.