When homeowners compare softeners, the salt bag gets most of the attention. The electric meter and the drain line get very little, yet both show up on the bills for as long as the unit stays in the house.
What the softener draws from the outlet
The control head stays plugged in around the clock, and the valve motor draws power each time it moves through a cycle. Ask the installer or manufacturer to put the unit's power rating in writing. Then check that the outlet is grounded, that it is protected, and that the unit cannot be unplugged by accident during a cleaning or a bump from the water heater work. The draw is usually modest, but it never stops, so it adds up across a year in a way the first invoice does not show.
What each regeneration sends down the drain
Each regeneration rinses the resin, pulls the brine through, and flushes the leftover salt water to the drain. The volume depends on how often the unit regenerates, how hard the supply is, and how many people use water in the house. Ask each provider two things: how the unit decides when to regenerate, and whether that setting can be adjusted. A unit that regenerates on a fixed schedule can waste water on days when the house barely ran a tap. Ask, too, whether the drain connection is dedicated or shared with a washer or sink, since a shared connection changes how the line handles the flush.
How these costs change the comparison
Put three running lines side by side on one page: salt, power, and water sent to the drain. A quote that lists only the purchase price and the salt will look cheaper than it is. For any estimate you receive, ask the provider to state its assumptions: the household size it used, the hardness figure it used, and whether the estimate counts drain water at all. If two estimates use different inputs, they cannot be compared until those inputs match.
Check your own bills before and after
Before you sign, pull a few months of your current water bills and note the usage figures. That gives you a baseline. After installation, read the water meter and the power bill on the same schedule and compare the results to the estimate. The gap tells you which assumption was wrong, and it gives you something specific to raise with the provider.
If you are narrowing a shortlist, the Best Water Softener Companies in St. Louis ranking is a reasonable place to start. Put the same running-cost questions to every company on it, and do not accept a quote that answers only the purchase question.