Richard Wright twice denied Tommy Smith, while Scott Loach repelled Town's best efforts most notably from David Norris and Alan Quinn.
Watford made the better start with Jack Cork having an early shot deflected wide, Jobi McAnuff sending a glancing header wide and David Wright's fine block denying Don Cowie.
Ipswich then had a decent spell but Jon Stead, Tommy Miller and Giovani Dos Santos all had efforts off target, with the latter limping off soon after.
Town appealed for a penalty when sub Danny Haynes' cross hit Lloyd Doyley's arm but the claim was rejected, before Norris drilled a 20 yarder just wide.
Smith had a great chance on 38 minutes when he robbed a dithering Ivan Campo, but Richard Wright made a fine block.
Town had a great chance early in the second half when Stead played in Norris, but Loach half-blocked his shot and Adrian Mariappa hooked it clear.
Richard Wright made a fine diving save to tip away a Smith curler, before Haynes went straight up the other end, surged into the box, and shot inches wide.
Loach blocked a fierce Norris drive, brilliantly tipped a Quinn shot round the post and blocked a Stead drive as Town turned up the pressure.
However, Watford held on to make it nine games unbeaten against Ipswich, having come into this match with seven straight wins in their previous meetings.