Answer
Yes, it is possible.
$v = \sqrt{gr}$ is the minimum speed.
Work Step by Step
If the speed is fast enough such that, at the top of the swing, the gravitational force is equal to the centripetal force, then the water will not fall out of the bucket. Therefore:
$m\frac{v^2}{r} = mg$
$\frac{v^2}{r} = g$
$v = \sqrt{gr}$, where $r$ is the radius of the circle.
Therefore, $v = \sqrt{gr}$ is the minimum speed.