Abstract: A control system for maintaining the liquid levels in a plurality of reservoirs connected in series includes one or more nested control modules. The nested control module, one for each reservoir, includes a proportional only level controller in electrical communication with the respective level sensor of each respective reservoir and is adapted to produce an output that becomes a set point for one or more respective PID flow controllers adapted to control the respective outflows of said respective reservoirs. The control system results in maintaining liquid levels in the reservoirs while substantially eliminating flow and level oscillations.