That's... surprising. To be clear, I'm not saying I don't believe you. But I'm definitely surprised - I've got a Series 2 which I get wet every day and even use while swimming and I haven't had any issues. My mother has a Series 2 or 3 which she also regularly uses while swimming.
Per Apple's documentation[0]
> Apple Watch Series 2, Apple Watch Series 3, and Apple Watch Series 4 may be used for shallow water activities like swimming in a pool or ocean.