What Size Water Softener for Well Water With Iron?
The number
96,000 grains or more, for 4 people at 15 gpg with 3 ppm of iron. That works out to about 56,700 grains of hardness a week, sized to regenerate roughly once every seven days.
Iron does two separate things to this calculation and most sizing advice only mentions one of them. It restricts which units are eligible at all, and it inflates the capacity you need, because resin treats dissolved iron roughly like four times its measure in hardness.
The 3 ppm modelled here adds about 12 gpg on top of the water hardness before any sizing happens. That is why the recommendation below is larger than a four-person household on city water, despite being the same four people.
At this iron level you are close to the threshold where a dedicated iron filter ahead of the softener becomes the better build. Above roughly 3 ppm the filter usually wins, because a softener absorbing iron permanently gives up resin life to do it.
Resin life is the real cost here. On iron-bearing water it drops from the 10 to 15 years municipal supply gives you down to as little as 5 to 10, so budget a rebed sooner and use a resin cleaner from the first month rather than after hardness starts returning.
What this size costs to run
A family of four gets through roughly one 40-pound bag of salt a month, which is the figure everything else scales from. At 4 people that works out to about 1 bag a month, so roughly $60 to $120 a year at $5 to $10 a bag. Iron pushes that higher than the household size alone suggests, because the resin is doing more work per gallon and the unit reaches its capacity sooner.
At 56,700 grains a week against a 96,000-grain unit, expect regeneration roughly every 9 or 10 days once the head has learned the household pattern. Each cycle also sends water to the drain, between about 21 and 55 gallons depending on the unit, which is worth checking against the spec if you are on a septic field.
Salt is the running cost that people notice. The one they miss is resin, which lasts 10 to 15 years on municipal water and 5 to 10 on iron-bearing well water, and costs $200 to $400 to replace. On this water plan for the shorter end of that range and budget accordingly.
Units that fit this size
No unit we track covers this capacity yet. The full comparison chart shows everything specced.
Your numbers are not these numbers
This page assumes 15 gpg and 3 ppm of iron. Hardness varies enormously between water supplies and it moves the answer more than one extra person does, so run your own figures.
What size water softener do you need?
Recommended capacity
96,000 grains
4 people × 75 gal/day × 27.0 gpg (iron-compensated) = 56,700 grains/week, sized for one regeneration per week at usable capacity.
No unit we track comes in this size yet.
Where to go next
Once you have a capacity, the cost guide shows what that size runs and why identical capacities vary by three times in price. If you have not decided on type yet, salt-based vs salt-free comes first, because a conditioner does not soften water and this calculation does not apply to one.