To start straight with, the waterproof material we use in order to ensure life lasting jewelleries is stainless steel. To be waterproof, whether stainless steel should be worn in the water or not depends on a variety of things.
One of the more common grades of stainless steel for creating components that is waterproof and so that will hold up well when exposed to water but not submerged in it is 304/L and this is the material we use for all our jewelleries making them all waterproof. 

With stainless steel, we are happy to offer a range of waterproof jewelleries that sparkles beautifully, giving your ensemble a touch of sophistication.

But the fact that stainless steel is incredibly durable and waterproof is just one of the many reasons we adore it.
The sort of stainless steel that you are wearing actually makes a difference for the waterproof resistance. The water from a shower will never corrode stainless steel of high quality.
It won't corrode or rust in the shower, so you can wear it without concern.
It will continue to look brand new for as long as you wear it.