There are some water resistant hearing aids that function better when they get a little wet.
But water resistant is not the same as water proof so the water resistant hearing aids are not meant to get really wet but can handle getting a little rain on them.
It's best though if possible to remove the hearing aids before you shower or go out in the rain and then put the hearing aids back in your ears after you get out of the shower or the rain.
If you get moisture in the hearing aid you can remove the moisture by removing the battery and leaving the battery compartment open.
Then set the hearing aids in a bag of rice which can help absorb the moisture and then they should work again.