Pumps, Pump Systems, and Water Treatment
This domain tests the arithmetic and the water chemistry: sizing a pump to the actual head it will see, setting controls and pressure tanks correctly, and choosing treatment that matches the test results rather than a catalog page.
Sizing the pump
- Total dynamic head equals the pumping level below the surface, plus the elevation of the discharge above the surface, plus pressure head at 2.31 feet per psi, plus friction loss in pipe, fittings, and the pressure tank manifold.
- Size to the pumping level, not the static level. A pump chosen on static water will run dry as the well draws down.
Controls and tanks
- Set tank precharge about 2 psi below the pressure switch cut-in, and size drawdown so the pump does not short-cycle. A cycle stop valve or constant-pressure controller holds steady pressure without cycling on every tap.
Treatment matching
- Low pH: calcite neutralizer or soda ash feed. Iron and manganese: oxidation followed by filtration. Hardness: ion exchange softener. Nitrate: reverse osmosis or anion exchange. Arsenic: adsorptive media or reverse osmosis, with speciation and competing ions checked. Radon: aeration. Bacteria: UV rated for the flow, always after sediment and pretreatment, since turbidity shields organisms.
Worked example
Pumping level 120 feet, discharge 20 feet above grade, 40 psi required, friction 15 feet. Pressure head equals 40 times 2.31, about 92 feet. Total dynamic head is 120 plus 20 plus 92 plus 15, or 247 feet. Choose a pump that delivers the target flow at 247 feet, not one that only meets the flow at zero head. If only the static level is used, the pump runs dry.
Traps that cost marks
- Skipping friction loss or using static level.
- Setting tank precharge at the cut-in rather than below it.
- Putting UV ahead of sediment filtration.
- Selecting arsenic treatment without testing for arsenic species and competing ions.