Losing at home to their West Country rivals is hard enough to bear but this was also Bath's sixth defeat in a row in all competitions.
A meagre losing bonus point leaves last year's free-scoring Premiership finalists languishing in ninth position, having lost seven of their 10 league games. Their points came from an early Dom Day try and two penalties by full-back Tom Homer.
Gloucester were pummelled in one corner of the Rec for almost the entire first 15 minutes as they conceded a string of penalties at maul and scrum.
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Referee Matthew Carley's patience was stretched too far and he sent second row Tom Savage to the bin in the 11th minute for diving under a maul.
Bath took advantage straight away, again relying on their catch-and-drive to give Wales lock Day his first try of the season, although Homer was wide with the conversion.
When Gloucester did get their attacking game under way, however, dropped balls and forward passes handed possession back to the home side.
Away fans' hearts were in their mouths when Kyle Eastmond put in a rolling kick to the corner but wing Steve McColl took a quick but ill-directed throw to full-back Billy Burns. He was caught in possession behind his own line, gifting Bath a five-metre scrum.
Gloucester stopped No 8 Leroy Houston from muscling his way over but only at the expense of a penalty kicked by Homer with 19 minutes on the clock.
The heavy drizzle and soggy conditions underfoot blunted Bath's attack but they showed impressive line-speed when Gloucester were in possession. When scrum-half Rob Cook got fingers to a pass from opposite number Willi Heinz, however, Hook knocked over the visitors' first points from 40 metres on 28 minutes.
Five minutes from half-time, the Welsh playmaker had another more difficult chance from wide out on the left but the ball fell short and was cleared by the hard-working Matt Banahan.
More encouraging for Gloucester was the squall that blew straight into the Bath players' faces as they returned for the second half. It was no problem for Hook to land his second penalty from 40 metres but Homer defied the elements at the other end to make the score 11-6 after 47 minutes.
An ill-advised offload by Semesa Rokoduguni and an ambitious chip and chase by Horacio Agulla on Bath's other wing, showed little appreciation of the conditions.
Forced onto the back foot, they conceded two more penalties in quick succession and Hook kicked both to put his side ahead for the first time on 56 minutes.
A long rolling kick by the Welshman had Bath in trouble again as Agulla was caught in possession and conceded a penalty. The kick was wide out on the right, however, and faded past the post.
But he could not miss from in front of the posts on 65 minutes. First Alafoti Faosiliva was robbed by Matt Kvesic and then Heinz made a piercing break and Bath gave away at the breakdown.
Bath simply could not mount any meaningful pressure of their own and looked even more rudderless once skipper Stuart Hooper went off. It could have been worse, but Hook was wide with another penalty attempt.
Bath never really looked like scoring, despite their frenetic efforts in the last 10 minutes. A line-out offered a faint chance in the final seconds but Kvesic pounced again to win a penalty at the breakdown to end all doubt.
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