Adam Mark Battensby threw the water bottle towards the pitch on October 2 last year, when Leeds beat Watford 1-0 during a Premier League clash.
The 31-year-old appeared at Leeds Magistrates' Court where he pleaded guilty to the charge.
Battensby, of Monckton Road, Pontefract, was cleared of assaulting a male at Elland Road on the same day.
However, he was given a four-year banning order to keep him away from football grounds.
He was also fined £498 and told to pay £105 costs.