The Hornets were seconds away from ending Leicester's winning run with an unlikely victory when Danny Drinkwater found the top corner to deny Watford all the points.
A draw was a good result nonetheless and manager Giuseppe Sannino will now be after a second straight home victory.
The Italian is still without Lewis McGugan, but Daniel Pudil could be back in the starting lineup for the visit of the Blues, who are on a high after their first league win since December on Saturday.
The reverse fixture between these two was on the opening day of the season when Troy Deeney scored the one and only goal.
Possible starting lineups
Watford: Almunia; Cassetti, Angella, Ekstrand; Anya, Battocchio, Tozser, Murray, Pudil; Deeney, Forestieri
Birmingham: Randolph; Caddis, Martin, Packwood, Robinson; Adeyemi, Huws; Burke, Novak, Lee; Macheda
Sports Mole says: 2-0