Ings scored for the fourth match in a row for the first time in his career -- his seventh goal in his last nine league outings -- when he met James Ward-Prowse’s free-kick for the opening goal on 22 minutes.
The goal broke open what had been a cagey start for both sides, who entered with the possibility to climb out of the bottom three with a positive result.
A desperate Saints then doubled their lead from a second dead-ball situation nearing the break after Ryan Bertrand slotted home from a Ward-Prowse corner-kick from close range.
Norwich, who has just one win from their last 49 attempts after conceding the first goal, avoided disaster with Ings dragging a shot wide before pulling one back through Teemu Pukki on 65 minutes.
Emi Buendia headed agonisingly wide of the post in added time with Saints hanging on for all four minutes to secure back-to-back home wins.
Southampton: McCarthy, Bertrand, Bednarek, Stephens, Cedric, Hojbjerg, Ward-Prowse, Redmond , Djenepo (Romeu 72), Long (Yoshida 85), Ings (Adams 77)
Unused subs: Gunn (GK), Danso, Obafemi, Boufal
Goals: Ings (22), Bertrand (43)
Bookings: Djenepo (59)
Watford: Krul, Byram, Godfrey, Zimmermann, Aarons, Trybull (Tettey 45), Amadou (Stiepermann 45), Hernandez, McLean, Cantwell (Buendia 84), Pukki
Unused subs: Fahrmann (GK), Vrancic, Srbeny, Lewis
Goals: Pukki (65)
Bookings: Byram (62)