I'll add my 5cents :)
For "tomber à l'eau", Caroline said it good, it means that what you expect will not happen (I planned to eat with Tom at noon but he said he couldn't be available > Mes plans tombent à l'eau)
For "virer à l'échec", it's more about that: some agreements/negotiations which fails - depending to the tense
Cela vire à l'échec > it's failing
Cela pourrait virer à l'échec > It could fail
Cela virera à l'échec > It will fail
Hope it helps