Can Apple fixed an iPad that was submerged in water

Water and electronics do not make happy bedfellows. Your iPad is not designed to be water resistant. While it may survive being splashed with water if immediately dried, it will almost certainly suffer irreparable damage if submerged.

You would be best advised to take your iPad along to the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to assess your iPad. If repair isn’t possible, the iPad can be responsibly recycled - and you’ll be in the best possible place to explore possible replacement:

Genius Bar Reservation and Apple Support Options - Apple

While your iPad is unlikely to be repairable, should you have benefit of any active AppleCare+ plan, your iPad will be covered for accidental damage - including water damage. AppleCare+ is an optional insurance product for your iPad - available within 60-days of purchasing your iPad.

If you don't have an AppleCare+ plan, check your domestic home insurance - as this might provide cover for accidental damage to your iPad or devices/appliances.

Your iPad has been catastrophically damaged.

Start here if you wish.

iPad Repair & Service - Apple Support

No.

Water damaged devices can’t be fixed.

They get replaced.

The warranty doesn’t cover water damage.

You will have to pay for a replacement.