Goals from Mark Yeates and John Eustace, one in each half, helped the Hornets condemn their hosts to their worst losing sequence in almost two years, as Brian McDermott's Royals struggled for consistency and quality throughout.
And Watford, who were without a league win going into the clash, took maximum advantage.
Reading were given all the early warning signs they could possibly need when Andres Weimann ghosted in behind Joseph Mills after five minutes.
However, the Austrian could only drag his shot wide of Royals goalkeeper Adam Federici's far post from the edge of the area.
Federici was forced into his first save of the afternoon after nine minutes as he kept out Mark Yeates' well-struck free-kick.
But the American stopper could do nothing about Yeates' dead-ball effort three minutes later, as the midfielder curled a 25-yard set piece over the wall and into the bottom corner.
Watford dominated the early exchanges, with Jonathon Hogg seeing his shot saved by the busy Federici and Reading struggled to get a foothold on proceedings.
Mills' deflected free-kick, which drifted out for a corner, and Mathieu Manset's wayward header were the closest the Royals got in the opening half hour, while Watford's Yeates again tested Federici from distance.
The home fans made their displeasure known as the teams went in for half-time, but McDermott's Reading failed to improve the mood inside the Madjeski in the second period.
John Eustace doubled Watford's advantage with a simple six-yard tap-in after 51 minutes - the Hornets' captain's first goal of the season -
after James Pearce failed to clear, and the away side were able to control possession against slapdash opposition.
The home midfield lacked conviction in their passing and chances were few and far between, with Mikele Leigertwood firing well wide midway through the second half and Hal Robson-Kanu also failing to trouble Scott Loach with a hugely speculative effort.
The longer the game went on the more desperate the home side became, with Mills wildly off-target with a free-kick in the dying moments.
That meant Watford were able to saunter to three valuable points, but for McDermott and his beleaguered Reading team the alarm bells will be ringing loud and clear as they find themselves in the relegation zone.