Waterproof watch cases do not in principle exist. Watch cases can be made water resistant using a variety of different materials, designs and techniques.
"A watch designed to withstand immersion to a depth of at least 100 m and to satisfy requirements specified in ISO standard 6425.
N.B. according to this standard, only the hundreds of metres have to be indicated on the watch.v. water-resistant watch, water-resistance." (Berner)