Like we said, the manufacturer will specify the IP rating of their product, and this should be a good guarantee as long as the manufacturer is reliable. However, phones are expensive devices and it’s smart to test the case yourself before putting the phone in. There are several ways to do this, but it’s probably the easiest with some paper tissues or cotton wool. You take a few pieces, place them inside, and close the case. Then you submerge it and leave it like that for a few hours. When you take it out, the content of the case should be dry. If that is the case, then you can have peace of mind that your phone will stay dry too.