OK grade Z horror movie makers, here's my idea. You can have it.
As people are opting more and more for cremation, the severity of a zombie apocalypse is quickly deteriorating to a 'zombie problem'.
But what if the ashes / cremains came back & blew in the wind like in dustbowl times and people couldn't keep them out of their homes, off their bodies & out of their noses, mouths and lungs. The powdered zed could wreak havoc on the warmie flesh bags from within.
And since people are so fond of dumping people's cremains into rivers, lakes & oceans, they could come in in liquified states via beaches, river beds and even through the plumbing.
When you combine this double whammy ~ boy fucking howdy ~ ZOMNADO !!.