What happens if you let water in your ear when you have a hole in your eardrum?

Infection: Shower or pool water - probably nothing, maybe infection. River, lake, ocean - definitely infection.

Water in the ear: Sometimes, nothing happens. Often, it is uncomfortable since water does not feel good when it's in the middle ear. It's kind of like water going up your nose. Sometimes, the bacteria in water that contaminates the ear can infect the ear. Then, the infected ear will drain and often be uncomfortable. That will require antibiotic ear drops.