Many homeowners look at the water bill after a softener goes in and assume the only new cost is salt. Regeneration also sends a volume of water to the drain each cycle. Whether that water shows up as a separate charge depends on how your utility bills sewer service. The softener does not set the rate. It only sets how much water goes down the drain and how often.
Check how your sewer charge is calculated
Find the rate sheet or the bill explanation from your water utility. Look for whether sewer is billed on metered water use, billed as a flat fee, or based on an average from a set period. If sewer is billed on metered use, a softener that regenerates often adds to that charge. If sewer is a flat fee, regeneration water will not change it, although the softener may still matter for other reasons.
What drives the volume
Three things set how much water a softener sends to drain. The first is how often it regenerates, which depends on how much water your household uses and on the hardness setting. The second is how much water each cycle uses, which depends on the valve, the tank size, and the rinse and backwash settings. The third is the hardness setting itself: a setting higher than your water needs wastes salt and water on every cycle, while a setting lower than needed leaves hard water at the tap.
Compare the settings before you blame the unit
Ask the installer or service company what hardness and regeneration settings were programmed, and why. Ask whether the controller regenerates on a timer or only when water use calls for it. Demand-based controllers can cut cycles when the household uses less water, but they need a correct setting to work well. Compare your own bills from before and after the install, not a number from another home.
Where the ratings help
When you compare models, look at how each one is rated for water efficiency and salt use, and check that those criteria match what your household needs. The St. Louis ratings page lists the scores, and the methodology page explains how each criterion is weighted, so you can see what a higher score is measuring before you choose.