All of this "space drive" stuff aside ... the primary motivation for this video is to demonstrate that a rotating wheel of water, with a controlled "leak", presents the kind of unbalanced force that one can only attain via the application of an "outside force", which in this case is Centrifugal Acceleration occurring inside the wheel.
It is very unfortunate that generations of students have conflated "outside force" with "outside of the container" (though most of the time the terms are admittedly interchangeable).

Normally a balanced rotating body that loses some of its mass will encounter an acceleration of its axis in the direction opposite of the flight path of the lost mass (due to the sudden condition of imbalance) but in this system the centrifugal force works with the water still in the wheel to maintain even distribution of mass and prevents imbalances in the same manner as a LeBlanc Balancer such as are used today in washing machines and some industrial/automotive capacities.