Is the iPhone 8 water resistant or waterproof

Water Resistant to a certain degree. Do not intentionally submerge it. Warranty does not cover water damage.

See here for details: About splash, water, and dust resistance of iPhone 7 and later - Apple Support

It’s designed to a water resistance standard and should meet that standard when new or when it’s been serviced and a new adhesive seal is used. However, production units aren’t tested, and in any case the resistance is reduced over time for any number of reasons. Apple makes no guarantees that it will keep water or humidity out.

Resistant.

None are waterproof.