Do all religions talk of the flood?

No. In the Tigris/Euphrates valley of the Middle East, an ancient flood legend evolved, coming down to us in the Epic of Gilgamesh and eventually in the biblical Flood story. Probably many other Middle Eastern religions borrowed the Gilgamesh flood story, but an equivalent story is not found in the Egyptian, Greek, Etruscan, Roman or Celtic religions. Nor is one found in the ancient Asian or African religions.