I have found a free version of "Here Comes the Flood" for the piano, on 10 Miles from Nowhere's Blog - you just need to scroll down to the bottom and you will see the link.
This is a hard song to find for free, but there are paid versions on MusicNotes.com and Sheet Music Direct. I've just included those for you in case there is anything incomplete about the free version. I don't play piano, so could not test this for you unfortunately, but I am a big Genesis fan, so let me know how you get along!
Peter wrote the song after leaving Genesis and claims that the song 'wrote itself'. It is about a mental flood apparently, a release.
Peter got his inspiration from a dream in which people could read each other's minds and the song is based on the fact that if that were to happen, only honest, open people will survive, whilst the others will be exposed for being liars and untrustworthy people.