The Hornets created very little after Alex Merkel's first-half volley forced Marek Stech into a smart stop and they came away with their eighth away draw in their last nine on their travels in the Championship.
The Italian shuffled his pack and made four changes, including resting the likes of Sean Murray, and he said their 11th match in 45 days was a game too far.
"I said before that my lads are playing a lot of games in a short time and in my opinion this is the main factor," he explained.
"It is not an excuse but maybe the fatigue had set in because we have been playing a lot of matches. There was a lot of supporters from Watford here and maybe they deserved a little more from us.
"Because we are playing a lot of games in a short time it is vital to me to give the players time to recover and pick the best 11 for the game. I gave Murray a little rest because we always play with him in the midfield and I would like to choose something different.
"We always play to win the game because we want to give back to the supporters what they do for us and in the second half it was tough on a heavy pitch and maybe we were tired."
In the last two months alone Watford have drawn at the likes of Leicester, Ipswich and Bournemouth and Sannino knows they have to turn those away single-point hauls into victories if they are to close the gap on the play-offs.
"When you can't win you are not to lose," he said. "As a coach I would like to win always, but I would like to change our trend in away matches."
The final whistle blew amongst furious appeals from Davide Faraoni after his cross seemed to hit Jamie McAllister's hand, but referee James Adcock waved away his angry protest.
Sannino said: "The lads said to me in the dressing room that it was a handball but I want to look forward and I do not want to blame the referee."
Gary Johnson's men kept Hornets goalkeeper Manuel Almunia busy throughout, the former Arsenal shotstopper denied James Hayter and Joe Ralls while Joe Edwards screwed a guilt-edged chance wide in the opening 15 minutes.
And despite the sense of frustration amongst some supporters at their failure to win three points on home soil once again, Johnson spoke of his pride at a display which saw them restrict Watford to very little.
"Other than not scoring a goal there was nothing disappointing about that display," he said. "We've got to keep solid and keep together and find a game that creates chances at this level and we did that.
"I'm honest and I wasn't disappointed, we played well. There was a lot of endeavour and work-rate.
"I'm not doing this just to build them up - that is the sort of game I can be confident with for the rest of the season.
"We are creating the openings but we are coming up against teams who want to get to the Premier League and that is a reality check.
"I'm going home absolutely proud of the football club and I'm looking forward to Saturday's game."
That match this weekend is a vital clash with 20th-placed Doncaster at Huish Park on Saturday before a daunting trip to Reading as they look to close the six-point gap between themselves and safety.
"If we can win two games on the trot we are back in the race," Johnson added. "That performance makes me a little bit more confident we can steal points at tough places.
"This is a massive game for us on Saturday and hopefully we can get that goal early."