H2O just add water lockets: How are they waterproof?

Question

I found the lockets from the T.V Show hit H2O just add water and they are sterling silver, but it said that they were not waterproof. And when watched the show, I saw that the locket/necklaces were waterproof or something because they swam with them. So, could someone please tell me either why they were not damaged in water or how to make sterling silver waterproof?? Thank you!!

P.S

(If possible) I wanted to swim with mine, but I knew that it would damage it.

Answer 1

cover the openings with wax

Answer 2

its tv... they may very well be made out of something else.... or lets be honest one swim with it  you won't notice it ruined and its tv so they have enough money to buy another