Fluid flow control for water treatment systems

A method of controlling a fluid flow rate, comprising:

• providing a fluid to a fluid containment tank structured to enclose a first interior space to contain the fluid;
• providing the fluid from the fluid containment tank to a receiving tank fluidically coupled to the fluid containment tank and structured to enclose a second interior space to contain the fluid;
• and
• controlling a flow of the fluid through a flow controller fluidically coupled to the receiving tank by changing a position of an internal volume of the flow controller along a vertical direction and relative to (1) a position of the receiving tank and (2) an upper level of the fluid in the fluid containment tank, wherein a change of the position of the internal volume adjusts a hydraulic resistance of a path from the fluid containment tank to an outflow port of the flow controller through the internal volume,
• wherein the flow controller is configured to perform one or both of:
• increase the flow rate when a distance between the position of the internal volume of the flow controller and the position of the receiving tank decreases in the vertical direction and a height between the position of the receiving tank and the upper level of the fluid in the fluid containment tank is held constant in the vertical direction,
• decrease the flow rate when a distance between the position of the internal volume of the flow controller and the position of the receiving tank increases in the vertical direction and a height between the position of the receiving tank and the upper level of the fluid in the fluid containment tank is held constant in the vertical direction.