This chapter presents the basic oft-used daily operational calculations along with engineering calculations used for solving more complex computations. It discusses water source calculations that apply to wells and pond/lake storage capacity. The chapter also discusses specific well calculations including well drawdown, well yield, specific yield, well casing disinfection, and deep-well turbine pump capacity. The calculations pertaining to well pumps include head, horsepower, and efficiency calculations. The two common tank shapes of sedimentation tanks are rectangular and cylindrical. The chapter shows the equations for calculating the volume for each type tank. Surface overflow rate calculations do not include recirculated flows. The chapter shows the equation for percent of product water used for backwashing calculations. Bed expansion is determined by measuring the distance from the top of the unexpanded media to a reference point (e.g., top of a filter wall) and from the top of the expanded media to the same reference.