The iPhone 7 is something called IP67 rated.
That means (roughly) that the phone is supposed to be waterproof up to 1 meter for up to 30 minutes.
So I don’t have the disposable income OR the inclination to test that out myself (plus I really like my headphone jack), but the guys over at RedmondPie.com found a video of somebody who did:
iPhone 7 Goes For Scuba Diving Test, Records 4K Underwater [Video] | Redmond Pie
Apple’s iPhone 7 is claimed to be IP67 rated, making it suitable for water resistance at a depth of 1m for up to thirty minutes. That’s great if you happen to drop your iPhone in the bath, or for some reason, feel the need to reply to emails in the shower, but there will always be someone who takes things a little bit further.