This app was mentioned in 5 comments, with an average of 1.40 upvotes
Here is a app if it fails this it's not waterproof don't try. If it passes your call, I took mine in the shower every day for two years, yours might not last five minutes. just wiping the phone with water should be fine
To add to this:
As u/KbaBBroS said, waterproofing can be checked here https://play.google.com/store/apps/details?id=gowiththejoe.xperiawaterresistance
Battery life on the Z3 is capable of lasting a whole day, and the Z3C is said to have battery longer than the former. Should be good enough for more so.
About the SD card, any will work... But apparently, a Class 10 is recommended for 4K recording. Other than that, anything will do.
Get a magnetic charger, so as to protect the cover of the charging unit cover (the rubber comes of over time). Turn off Microphone Noise Suppression, apparently it affects microphone quality a lot. Use STAMINA mode, it's great of extending battery on lighter use. Android
Enjoy your Z3C, it's a good choice :D
To test the water resistance you can use this app from Play store: https://play.google.com/store/apps/details?id=gowiththejoe.xperiawaterresistance
The same thing can be found from inside the service menu on the phone, but it's considerably harder to find.