Greater Anglia operates a train from Colchester to Watford hourly. Tickets cost $24 - $35 and the journey takes 52 min. Alternatively, Green Line (operated by Arriva) operates a bus from Colchester to Watford every 30 minutes. Tickets cost $13 and the journey takes 2 h 22 min.
From Colchester train to Liverpool Street Underground Station then Tube to Watford Underground Station. 2 h 1 min £26. From Colchester Town Centre, St. John's Street bus to Chelmsford City Centre, Railway Station, line 59 bus to Harlow Town Centre, Bus Station (Harlow Bus Stn), then bus to Watford, Town Hall. 5 h 10 min £15. From Colchester drive to Watford. 1 h 17 min £14.