"Water on the ear" is a colloquial expression which refers to getting water in your ear, and the water gets trapped in the ear canal. The water trapped in the ear canal can cause an earache (discomfort or pain in the ear), nausea, dizziness (because our sense of balance is in the ears), loss of clarity of hearing, and sometimes infections. Swimmers frequently have this problem, and for that reason some people call this ailment "swimmer's ear." In icespirit's sentence, "water on the ear" is used figuratively, not literally. That is, someone talks and talks and talks and talks so much that you are overwhelmed, and suffer some or all of these or similar symptoms: boredom, dizziness, fatigue, or the inability to hear clearly. Personally, I think the analogy of excess speech to water on the ear is inventive and humorous.

I'm a native speaker, and I have no idea what this means.

Like the others, I have never heard of this saying. The closest thing we have in English to this is the term "wet behind the ears" which means to be lacking in experience (ie The new employee is too young and wet behind the ears). Unfortunately this doesn't fit into the context that you are asking about. Sorry!

i guess it means that you stopped hearing them clearly bcuz they talked too much :/