A chlorine metering pump is a small positive-displacement pump that injects a measured dose of sodium hypochlorite into the well line every time water flows. It is the working heart of a continuous chlorination system, used on wells that carry bacteria, iron bacteria, or hydrogen sulfide that a filter alone cannot keep up with. Get the dosing and the contact time right and the rest of the system behaves.
What the pump actually does
The pump strokes a diaphragm at a set rate, drawing dilute bleach from a solution tank and pushing it through an injection quill into the pressure line, normally after the pressure tank and before the retention tank. It has to run only when water is moving, so it is triggered either by a flow switch in the line or by the well pump's own circuit. Stroke rate and stroke length together set the dose, and the two adjustments are independent, which is what makes a metering pump tunable rather than just on or off.
Contact time is the other half of the job
Chlorine does not act instantly. Bacteria need contact time in solution, and the oxidation of dissolved iron and hydrogen sulfide into filterable particles also takes minutes, not seconds. That is why a chlorination setup pairs the pump with a retention tank sized to hold water long enough at the household's peak flow. Undersize the tank and you get chlorine odor at the tap with iron still dissolved and passing through. The pump and the tank are one design decision, never two separate purchases.
Sizing, solution strength and drift
Dose is set by the demand of the water, not by a rule of thumb: raw water heavy in iron or sulfide consumes chlorine before any residual is left for disinfection. Standard practice is to dilute household bleach in the solution tank so the pump runs at a comfortable mid-range setting rather than at either extreme, which gives room to adjust in both directions. Solution strength drops as bleach ages in the tank, so a dose that was right in spring drifts by late summer and needs checking.
Maintenance and what goes wrong
The failure list is short and repetitive: a calcified injection quill, a check valve held open by grit, an air-locked suction line, and a solution tank run dry so the system pumped nothing for a week without complaining. Test for a chlorine residual downstream at a fixed interval and log it, because a metering pump that has stopped dosing looks and sounds exactly like one that is working. Private wells are not federally regulated under the Safe Drinking Water Act, so nobody else checks this for you.
Where it sits relative to the filters
Order matters. Chlorine goes in first, contact happens in the retention tank, and the carbon or catalytic filter that strips the residual chlorine and the oxidized iron comes last, before the water reaches the house. Put a carbon filter ahead of the retention tank and it will destroy the chlorine before it has done any work. Our well water filtration guide lays out the full running order, including where a softener belongs when hardness is in the picture too.
Questions people ask about chlorine metering pump
Where does a chlorine metering pump get its signal to run?
Either from a flow switch in the pressure line or from the well pump circuit, so that dosing happens only while water is actually moving through the pipe.
Can I use plain household bleach in the solution tank?
Unscented sodium hypochlorite with no additives is the usual choice, diluted with water so the pump can run mid-range rather than at the end of its adjustment.
Do I still need a filter after the chlorination system?
Yes. Chlorine turns dissolved iron and sulfide into particles and leaves a residual taste, and a carbon or catalytic filter after the retention tank removes both.
How do I know the pump is still dosing correctly?
Test for a chlorine residual downstream on a set schedule and write it down. A pump with a blocked quill or an empty tank still runs and still sounds normal.