My Face ID was disabled immediately when my phone got in contact with water isn’t it supposed to be water resistant

Under perfect conditions, yes. However normal usage, flexing, being dropped, etc. can compromise the seals.

Take it to a Genius Bar to have it looked at.

Genius Bar Reservation and Apple Support Options - Apple

About Apple Watch water resistance - Apple Support

• About splash, water, and dust resistance of iPhone 7 and later - Apple Support
• Water and other liquid damage to iPhone or iPod isn't covered by warranty - Apple Support

Again:

• About splash, water, and dust resistance of iPhone 7 and later - Apple Support
• Water and other liquid damage to iPhone or iPod isn't covered by warranty - Apple Support

I have same question, they say "water resistant", but now i have a damage phone and who will be responsible (iPhone 11 pro) ? why they say something that is not the truth ?? no face id and a lot problems, touch screen problem, a green line, and more... if the phone is not water resistant should not tell that !!!

Read the previous posts about water resistance.

Me too i have a green line on my phone and face id is not working due to water