Pani vizhum malarvanam's scale is apparently a bit more complex.
I'm copy/pasting a post made by Vignesh Subramaniam on Orkut:
"The song's key signature is not D major. In fact you cannot define the key signature of this song via Western classical music. Its best to describe this song as the scale of carnatic 'Chala nattai'. As you know, Its a vivadhi ragam which employs R3 and Dha3. But it the 12 note system of Indian (and western) music this is mapped to Ga2 (i.e., the note F) and Ni2 (note C). And on top of this it has the regular Ga3 (i.e., F#) and Ni3 (C#); So by definition it has both F & F# and similarly C and C#. (Thats why I said you cannot classify the song as D major scale); Its also because of the same reason that the notes E and B are absent in the song's melody.
But presence of absence of a note in the scale of song has no influence over the chords used in the song. At least with Maestro this is more a rule than exception."
Basically I think it means this song is neither major nor minor scale!
Stop existing and start living!