iCloud backup

iCloud backups can only be done over wifi. If you don't have access to a wifi network you might be able to use another cellular device as a personal hotspot and back up via that

my iphone is fell down in water, it is not repairable

I searched and found the same basic solution several places: https://www.tech-recipes.com/rx/59467/use-cellular-data-back-iphone/ I am not sure if it works.