Test your water first — no exceptions on a well
Well water is not on anyone's quality report. Hardness varies well to well. On a well, test for hardness, iron, manganese, pH, and hydrogen sulfide before buying anything. Every number in this guide depends on a real test result — not a zip code lookup or a regional average.
Written from field experience: Alabama Grade IV Wastewater Operator. Sources: calcengineer sizing calculator (most standards-grounded), HomeWater101, WaterHardness.org, Discount Water Softeners, Lowe's, Aquasana, watersoftenersizing.com, NSF/ANSI 44. Compiled September 2026.
Quick reference
| Item | Value |
|---|---|
| ppm to gpg conversion | Divide by 17.1 · Example: 200 ppm ÷ 17.1 = 11.7 gpg |
| Iron adjustment | +5 gpg per 1 ppm ferrous iron — often the step that changes everything |
| Daily gallons per person | 50–82; 75 is the common working figure |
| Sizing formula | People × 75 gal × compensated hardness × 7 = weekly grain requirement |
| Treatment threshold | Commonly cited at 7 gpg; ≥10 gpg is "very hard" |
| The nameplate | Maps to resin volume at max salt dose — NOT usable delivered capacity |
| NSF/ANSI 44 salt efficiency floor | 3,350 grains per pound of salt (California: 4,000) |
| Valve type to buy | Meter/demand-initiated — not timer |
| Resin life, standard | 10–15 years (8% cross-link); 20+ years (10%+) |
| Resin life with chlorine | 5–7 years — city water users need to know this |
| Salt-free conditioner | Does NOT remove hardness — water tests the same before and after |
| Treatment sequence on well | Sediment → iron/H₂S filter → softener → point-of-use RO |
Step 1 — Get your actual hardness number
Everything in sizing flows from your hardness test. Don't size from a zip code lookup — hardness varies by well and by season, and a regional average can be off by half.
| Method | Accuracy | Detail |
|---|---|---|
| Liquid drop titration kit | Most accurate DIY | Test kitchen cold water tap. Inexpensive and reliable enough to size from. |
| Professional lab | Most accurate overall | ADEM-certified lab for Alabama wells. Covers hardness, iron, manganese, pH, bacteria. |
| Test strips | Rough | Good enough to confirm you have a problem. Not accurate enough to size from. |
| Zip code lookup | Do not use to size | Regional averages miss well-to-well variation. The softener costs far more than a test kit. |
| Hardness (gpg) | Classification | Softener decision |
|---|---|---|
| Under 1 | Soft | No treatment needed |
| 1–3.5 | Slightly hard | Usually no treatment |
| 3.5–7 | Moderately hard | Treatment optional — scale on heaters, spots on dishes |
| 7–10.5 | Hard — treatment threshold | Softener typically warranted |
| 10.5–14 | Very hard | Softener strongly recommended |
| Over 14 | Extremely hard | Softener essential |
Step 2 — The iron adjustment: the step that changes the answer most
2 ppm of iron can double your effective hardness — and nobody who skips this step gets the size right
Add 5 gpg of effective hardness for every 1 ppm of dissolved (ferrous) iron. If your water is 10 gpg hard with 2 ppm iron, size your softener as if your hardness is 20 gpg. A softener sized on raw hardness alone, on a well with iron, is undersized from day one — and will foul its resin bed over time.
| Contaminant | Adjustment | Note |
|---|---|---|
| Ferrous iron (dissolved, clear at tap) | +5 gpg per 1 ppm | The dominant convention across all sizing sources |
| Manganese | Compensation factor applies | Consumes resin capacity — test and apply separately |
| Ferric iron (orange particles at tap) | Not sized for — pre-treatment required | A softener is the wrong tool. Iron filter upstream. |
| Iron bacteria | Not sized for — pre-treatment required | Shock chlorination first. See iron bacteria guide → |
| Iron above 5 ppm | Dedicated iron filter upstream — regardless | Beyond the adjustment. The softener cannot handle it alone. |
The published iron factor ranges from 1 to 5. This guide uses 5 — the conservative dominant convention across the most widely cited sources. Using 1 risks a chronically undersized softener on an iron well. Size conservatively and add the iron filter if iron exceeds 5 ppm. See the iron + softener guide →
Step 3 — The sizing formula
The formula
Step 1: Daily use = people × 75 gallons per person
Step 2: Compensated hardness = hardness (gpg) + (iron ppm × 5) + manganese adjustment
Step 3: Daily grains = daily gallons × compensated hardness
Step 4: Weekly requirement = daily grains × 7
| Step | Calculation | Result |
|---|---|---|
| Household | 4 people × 75 gal | 300 gallons/day |
| Hardness | 10 gpg (from test) | — |
| Iron adjustment | 1.5 ppm × 5 | +7.5 gpg |
| Compensated hardness | 10 + 7.5 | 17.5 gpg (not 10) |
| Daily grains | 300 × 17.5 | 5,250 grains/day |
| Weekly requirement | 5,250 × 7 | 36,750 grains |
Without the iron adjustment, the same household calculates to 21,000 grains weekly — and would likely be sold a 24,000-grain unit. The iron pushes the real requirement to nearly 37,000 grains. That is not a marginal difference. It is the difference between two product categories.
The nameplate trap — the most important section in this guide
A "32,000 grain" softener does not deliver 32,000 grains in efficient operation
The nameplate grain count maps to maximum capacity at maximum salt dose — the least efficient way to run the unit. At an efficient salt setting (which minimizes salt cost and brine discharge), delivered capacity is meaningfully less. Sizing your weekly grain requirement directly against the nameplate will leave you short. Size against delivered capacity at an efficient salt setting. In practice, that usually means going one size up from what the arithmetic suggests.
| Setting | What you get | Trade-off |
|---|---|---|
| Efficient setting | Less salt per regeneration. Meets NSF/ANSI 44 floor of 3,350 grains/lb. | Less capacity delivered per cycle — need more resin for the same weekly output. |
| High capacity setting | More grains per cycle — closer to the nameplate number. | Less efficient with salt. Higher cost and more brine discharged. |
NSF/ANSI 44 — the efficiency standard
| Requirement | Value |
|---|---|
| Salt efficiency floor | At least 3,350 grains removed per pound of salt |
| Regeneration water limit | No more than 5 gallons per 1,000 grains removed |
| California requirement | 4,000 grains per pound — a higher bar than the national standard |
| What it covers | Residential cation exchange water softeners |
Salt-free conditioners vs real softeners — the honest distinction
"Salt-free water softener" is a marketing term, not a technical description
A salt-free conditioner (typically Template Assisted Crystallization — TAC) does not remove calcium or magnesium. After treatment, your water will test exactly as hard as before. TAC alters how hardness minerals crystallize so they are less prone to forming scale — a legitimate benefit for pipe and appliance protection. But if you want soft water, you need an ion exchange softener. Ask any seller directly: will my water test softer afterward? The honest answer from a conditioner is no.
| Salt-based softener | Salt-free conditioner (TAC) | |
|---|---|---|
| Removes hardness? | Yes — minerals leave the water | No — minerals stay in the water |
| Water tests after treatment | Near zero hardness | Same as before treatment |
| Scale protection | Yes | Yes — TAC's actual purpose |
| Soft feel, better lather | Yes | No |
| Brine discharge | Yes — check local rules | None |
| Salt required | Yes | No |
When a conditioner is the right choice: brine discharge is restricted (septic or local ordinance), your only goal is scale protection rather than soft water, hardness is moderate rather than severe, or there's no space or drain for a brine tank.
When you need a real softener: hardness is above 7 gpg, you want the soft-water feel and better soap performance, you have existing scale problems, or you want a measurable result you can verify with a test kit. See the salt-free conditioner guide →
Valves and configurations
| Valve type | How it decides to regenerate | Verdict |
|---|---|---|
| Timer/clock | Fixed schedule regardless of actual use | Do not buy — regenerates when not needed, runs out when demand is high |
| Meter/demand-initiated | Measures actual water use; regenerates when capacity consumed | Buy this — uses salt and water only as needed |
| Metered with reserve | Same as metered but holds back reserve capacity | Best — ensures you don't run out before the cycle runs |
| Configuration | Detail |
|---|---|
| Single tank | One resin tank. During regeneration the unit is on bypass — you get hard water for that period. Schedule overnight to minimize impact. |
| Twin tank | Two resin tanks alternating. Soft water available continuously, including during regeneration. Needed for round-the-clock demand or very high hardness requiring frequent regeneration. |
| Valve brand | The valve is the part that fails and the part that determines parts availability in 10 years. Ask what valve is inside and whether local plumbers service it. The Fleck valve is widely cited as the most proven in residential service. |
Resin life — the chlorine finding most buyers miss
| Condition | Expected resin life |
|---|---|
| Standard 8% cross-linked resin | 10–15 years under normal conditions |
| High cross-link (10%+) | 20+ years — resists chlorine better |
| With chlorine exposure (city water) | 5–7 years on standard resin |
| With iron fouling | Shortened — capacity degrades permanently before failure |
City water users: Municipal water is chlorinated, and chlorine cuts standard resin life from 10–15 years to 5–7. Two responses: specify high cross-linked resin (10%+), which reportedly lasts 20+ years and resists chlorine better — or install a carbon pre-filter ahead of the softener to remove chlorine before it reaches the bed. Either costs less than replacing the resin bed twice.
Salt types and bridging
| Type | Notes |
|---|---|
| Solar salt | Evaporated seawater. Common and inexpensive. |
| Pellet/evaporated | Higher purity, less residue in the brine tank. Most commonly recommended. |
| Rock salt | Cheapest, highest insoluble content. More brine tank cleaning required. |
| Potassium chloride | For sodium-restricted households or where chloride discharge is restricted. Costs more and is less efficient per pound. |
Salt bridging — a hard crust forming over the salt so it stops contacting water — is the most common cause of a softener that "stopped working." The brine tank looks full, the unit runs its cycle, and nothing gets softened because the salt isn't dissolving. Check by pushing a broom handle down into the salt. If it hits a hard crust with a void underneath, break it up. Check this before calling anyone.
Well water treatment sequence — order matters
| Position | Equipment | Why it goes here |
|---|---|---|
| 1st | Sediment pre-filter | Protects everything downstream. A $50 filter absorbing what would otherwise foul the softener. |
| 2nd | Iron and H₂S filter (if needed) | Must precede the softener. Iron fouls softener resin permanently — fouled resin cannot regenerate back to full capacity. See the AIO iron filter guide → |
| 3rd | Water softener | After pre-treatment. Bypass outdoor spigots — no reason to soften irrigation water. |
| 4th | Point-of-use RO (drinking water) | For drinking water quality concerns beyond hardness. The softener does not address them. |
One exception: If iron is under about 3 ppm and hardness is the only issue, a softener with iron-tolerant resin may handle both. Above 3 ppm, the iron will foul the resin and you need a dedicated iron filter upstream. See the full iron + softener guide →
What a softener does not do
A softener removes calcium and magnesium — that is its entire function. It is not a purifier, not a general filter, and not a treatment for most drinking water concerns. Any salesperson implying otherwise is overselling.
| Contaminant | Softener handles it? |
|---|---|
| Calcium and magnesium hardness | Yes — the entire function |
| Modest dissolved iron (<5 ppm) | Partially — if sized for it |
| Lead and heavy metals | No — needs NSF-certified lead filtration or RO |
| Bacteria and viruses | No |
| Nitrate | No |
| PFAS | No |
| Chlorine | No — and chlorine actively shortens resin life |
| Hydrogen sulfide odor | No — needs oxidation treatment |
| Arsenic | No |
| Sediment | No — needs a pre-filter |
Installation requirements
Location: After the pressure tank (on a well) and after any sediment or iron pre-treatment. On the main line to the house.
Bypass outdoor spigots: No reason to soften irrigation water — it wastes capacity and salt with no benefit to the lawn.
Drain with air gap: The brine discharge needs a drain. Air gap is a code requirement in most jurisdictions.
Consider bypassing the kitchen cold tap: Some households prefer unsoftened water for drinking and cooking. Easy to plumb a bypass during installation.
Pressure: Softeners do not increase pressure — they can slightly reduce it due to flow resistance through the resin bed.
Check brine discharge rules before buying. Some jurisdictions restrict softener brine discharge to septic systems or sanitary sewers — particularly where chloride loading on the drainfield is regulated. This is a real reason some households choose a salt-free conditioner instead. Verify locally before purchasing. This varies significantly by state and municipality.
Calculator
Water Softener Sizing Calculator
Includes the iron adjustment. Sizes against delivered capacity at an efficient salt dose — not the nameplate.
Your water test results
Enter 0 for iron if your test showed none, or leave blank.
Your household
Common mistakes
| Mistake | Consequence |
|---|---|
| Sizing without testing | Every number downstream is a guess |
| Ignoring iron in sizing | 2 ppm iron can double effective hardness — undersized from day one |
| Sizing against the nameplate | Maximum capacity at maximum salt dose — not usable delivered capacity |
| Buying a salt-free conditioner expecting soft water | Water tests the same hardness before and after |
| Buying a timer valve | Regenerates when you didn't need it; runs out when you did |
| Oversizing | Stagnation and channeling — water carves paths through resin and bypasses most of it |
| Undersizing | Frequent regeneration, more salt and water, hard water breakthrough at peak demand |
| Using softener as an iron filter | Fouls the resin permanently — capacity degrades before failure |
| Softening outdoor spigots | Wastes capacity and salt on irrigation |
| Ignoring chlorine on city water | Cuts standard resin life from 10–15 years to 5–7 |
| Not checking brine discharge rules | Some jurisdictions restrict it, especially on septic |
| Assuming it improves drinking water safety | Does not address lead, bacteria, nitrate, or PFAS |
| Not checking for salt bridging first | The most common cause of "stopped working" — free to check |
Questions to ask the seller
What is the delivered capacity at an efficient salt setting — not the nameplate?
What is the grains per pound of salt rating — the number that tells you running cost?
Is it certified to NSF/ANSI 44?
Is the valve meter-based or timer-based?
What valve is it, and who services it locally?
What resin — standard 8% cross-linked or higher?
Does my sizing account for my iron? Show me the calculation.
What pre-treatment do you recommend, and why?
What will this cost to run in salt and water per year, given my weekly grain requirement?
What is the warranty on the tank, the valve, and the resin separately?
Common questions
How do I size a water softener for well water?
Test for hardness and iron. Convert ppm to gpg (÷17.1). Add 5 gpg per ppm of ferrous iron. Multiply people × 75 gallons × compensated hardness × 7 for your weekly grain requirement. Size against a unit's delivered capacity at an efficient salt setting — not the nameplate.
What is the iron adjustment and why does it matter so much?
Add 5 gpg per 1 ppm of ferrous iron. At 2 ppm iron and 10 gpg hardness, size as if hardness is 20 gpg. A softener sized on raw hardness alone is chronically undersized — and will foul its resin bed over time.
Does a salt-free softener actually soften water?
No. A salt-free conditioner (TAC) does not remove calcium or magnesium — your water tests the same hardness before and after. It reduces scale formation, which is a legitimate benefit. But if you want soft water, only an ion exchange softener delivers it.
Should the softener go before or after the iron filter?
After — always. Iron fouls softener resin permanently. Correct sequence: sediment → iron filter → softener → point-of-use RO.
How long does softener resin last?
Standard 8% cross-link: 10–15 years. High cross-link (10%+): 20+ years. With chlorine exposure (city water): 5–7 years. Specify high cross-link resin or add a carbon pre-filter if you're on chlorinated municipal water.
Related guides
- Water softener for well water with iron — the full iron treatment sequence
- Air injection iron filter guide — what goes before your softener
- Salt-free conditioner guide — when a conditioner is the right choice
- Best water softeners for well water — reviewed and ranked
- Kinetico water softener review
- Well water pressure tank guide — what sits before the softener
- Well water testing guide — test before you buy anything