Top 3 Tips to Do with a Water-damaged iPhone with/without AppleCare
You have several choices to back up your iPhone. Go to iTunes and click Backup option in Summary section. I have to mention that iTunes always keeps the latest backup by replacing the previous one. If you want to keep backup files at different time points, I recommend you Tenorshare iPhone Care Pro. It backs up all iPhone/iPad/iPod data including photos/messages/contacts/notes/app data, etc. and keeps all backup files separately on local. In the future you can restore the backup to any new iOS device.