Hello,
i found this details about water resistance
Splash, water and dust resistance are not permanent conditions and resistance may decrease as a result of normal wear. Liquid damage is not covered under warranty
and
To prevent liquid damage, avoid:
- Swimming or bathing with your iPhone
- Exposing your iPhone to pressurised water or high-velocity water, such as when showering, water skiing, wakeboarding, surfing, jet skiing and so on
- Using your iPhone in a sauna or steam room
- Intentionally submerging your iPhone in water
- Operating your iPhone outside of the suggested temperature ranges or in extremely humid conditions
- Dropping your iPhone or subjecting it to other impacts
- Disassembling your iPhone, including removing screws
full article here :
About splash, water and dust resistance of iPhone 7 and later - Apple Support (IE)