unable to unpair watch with phone as water damaged

It won't show up on find my because the watch needs to be connected to the internet.

Navigate to iCloud.com from your computer's web browser to disable Activation Lock.

Sign in with your Apple ID and password.

Click on Account Settings.

Select your Apple Watch under My Devices.

Click on the X next to your Apple Watch to remove it.

Click Remove to confirm.

There really isn't much data on there because it's mostly kept on your phone,if you downloaded any music on the watch then that will still be there.If you are going to fix the watch then you could always erase it then.If you are trashing the watch then I wouldn't worry about it as you said it won't turn on.

What you have done is to prevent any nasty surprises when you pair a new watch to your phone by removing the activation lock.