What if your water breaks at 20 weeks can the baby survive?

No they can not. There has been a few cases in this world but in general no.

The question was water breaking, not birth. Yes, your baby can survive. The hospital will put you on bed rest, repress birth with drugs and inject you with steroids to promote faster growth. As long as you can hold of giving birth for as many weeks as possible, there is a good chance the baby can survive.