"The FAA intends to look into whether any planes approaching O'Hare at the time of the incident may have leaked water. ... Still, it is not the only answer, FAA spokesman Tony Molinaro said. Though the skies over Chicago were clear Wednesday evening, airplanes that flew through damp clouds anywhere en route to the Midwest could have accumulated structural ice that gathers on surfaces and around gears, struts and tail sections of aircraft."
My seven years working in and around aircraft calls BS on that one, I've never seen "structural ice". Again speaking from experience that famous blue ice isn't water, just look in the bottom of a portable toilet! (;->)