What is when did your moms water break in french?

The literal translation of "when did your mom's water break" is:

Quand est-ce que l'eau de ta mère a rompu?

However, this is a very formal and awkward way to say it in French. It's much more common to say:

Quand ta mère a-t-elle accouché?

This translates to "When did your mother give birth?" which is a more natural and polite way to ask about the timing of a birth.