Lyric discussion by Blue_Man 

Cover art for Flood I lyrics by Sisters of Mercy, The

I think that this is a song on a couple of levels - the flood is a metaphor for passion, but also a physical flood following a nuclear exchange (on the album, this song runs straight on from Dominion/Mother Russia, which ends with Eldritch imploring "Mother Russia rain down, down. down!").

Cheery, eh?