Hatton Cross underground has a veritable stream running out of the
westbound platform wall into the gutter below the tracks. ....

I have stood many times at Hatton Cross and heard running water,
thought it was a running tap. I guess it must be just inside the
tunnel entrance. Maybe a tributary of the River Crane, as the track
rises briefly from the tunnel between Hatton Cross and Hounslow West
to go over that river.

Thanks for the information on Great Portald Street, guess Thames Water
have a leaking main above the station.