As said iPhone 7 is waterproof, but actually no phone is completely waterproof.
because iPhone is also worked with battery, which needs to be charged, and couldn't be wet with water.
Tips: when your iPhone is wet with water, you'd better spill out the water, and close your iPhone, then dry it.
then wait for about 12 hours, you can restart it to have a try, if it doesn't work well, you'll need to backup your iPhone data immediately, in case it won't work and we'll lost all our iPhone data.
Here, we can use iTunes and iCloud for help, also we can relay on third-party iOS data recovery software iRefone for help, it can help us backup and recover our lost data selectively.