How to Choose a Water Softener System
Choosing a home water softener comes down to seven steps: test, decide, size, check flow, pick a valve, plan the install and budget. Work through them and you'll know exactly which water softener system fits your home; if you just want our answer, the Aquasana SimplySoft 40K tops our best water softener rankings.
How to choose a water softener: the 7-step checklist
- Test your water. Use strips or a titration kit, or your utility's annual water quality report. On a well, get a lab test for iron, manganese, pH and sulfur too.
- Decide: soften or condition. If you want soft water (less soap, no spots), buy salt-based. If you only want scale protection and no salt, a salt-free water softener can work inside its limits.
- Size it in grains. People × 75 gallons × hardness (gpg) × days between regenerations, plus headroom. The calculator below does it.
- Check the flow rate. Add about 2 gpm per shower and 1.5 gpm per appliance that runs at the same time; the softener's rated flow should beat that.
- Pick the valve and layout. Metered (on-demand) valves save salt over timers. Cabinet units save space; two-tank units with a Fleck valve are easier to service.
- Plan the install. You need the main line, a drain with an air gap and usually an outlet. See water softener installation.
- Budget for running costs. Salt, water for regeneration, the odd cleaner and a resin rebed after 10–15 years. Our water softener cost guide adds it up.
Types of water softener systems (salt, salt-free, dual tank)
Salt-based ion exchange is the only type that actually removes hardness: resin beads swap calcium and magnesium for sodium (or potassium), then a brine rinse recharges them. Dual-tank systems are the same chemistry with two resin tanks, so one is always online. Salt-free conditioners use template-assisted crystallisation (TAC) to stop minerals sticking as scale without removing them. Magnetic and electronic "descalers" are a fourth category with weak evidence (see what a water conditioner is). All water softener systems in our rankings are point-of-entry: they treat the whole house.
Read your hardness test strip
How to read this: dip a hardness strip for a second, wait 15 seconds, then tap the pad colour that matches, or type the number your kit gives you.
Pick a pad or type a number to see your hardness class.
Water hardness chart: gpg, ppm and what to do
How to read this: find your test result in either unit. Classes follow the U.S. Geological Survey scale (mg/L as calcium carbonate); 1 gpg = 17.1 ppm.
| Class | ppm (mg/L) | gpg | What to do |
|---|---|---|---|
| Soft | 0–60 | 0–3.5 | A softener isn't needed for scale. Spend on a filter if taste is the issue. |
| Moderately hard | 61–120 | 3.6–7 | Some scale and spotting. A small softener or a salt-free conditioner fits. |
| Hard | 121–180 | 7.1–10.5 | Visible scale on fixtures and heaters. A salt-based softener is worth it. |
| Very hard | over 180 | over 10.5 | Heavy scale. Use a salt-based softener sized with the calculator; salt-free units usually fall outside their stated limits. |
Sizing a water softener system for home (grains per day)
Capacity is quoted in grains: the hardness a full resin bed can remove before it needs regenerating. A water softener system for home use should go about a week between regenerations. Too small and it regenerates every day, wasting salt and water; too big and the resin sits idle, which can let it channel or foul. Iron counts extra: add about 4 gpg for every ppm of clear-water iron.
How big of a water softener do I need?
Here is how to size a water softener in one line: people × 75 gallons × hardness (gpg) × 7 days, plus about 25% headroom. Common water softener sizes are 24,000, 32,000, 40,000, 48,000, 64,000 and 80,000 grains; round up to the next size. A family of four on 12 gpg lands near 32,000–40,000 grains; the same family on 20 gpg needs about 48,000. The calculator below does the maths with your own numbers.
Water softener size calculator
How to read this: we multiply daily water use by your hardness (plus iron), then by the days between regenerations, and add 25% headroom.
4 people × 75 gal × 12 gpg = 3,600 grains a day. Over 7 days with headroom you need about 31,500 grains, so look for a 32,000-grain softener.
Ranked picks with enough capacity: Kenmore 350 (32,000), Aquasure Harmony Lite 34K (34,000), GE Smart Water Softener 35K (35,000), Aquasana SimplySoft 40K (40,000).
Assumptions: 75 gallons per person per day; each ppm of clear-water iron counts as 4 gpg of hardness.
What makes a high efficiency water softener
A high efficiency water softener gets more hardness removal out of each pound of salt and gallon of water. Three things drive it: a metered (demand) valve that regenerates only when the resin is nearly used up; a lower salt dose per regeneration, since resin captures hardness most efficiently at low doses; and, on some valves, proportional or upflow brining, which refills only the brine actually used. NSF/ANSI 44 has an optional efficiency rating: a certified-efficient softener must deliver at least 3,350 grains of hardness removal per pound of salt and use no more than 5 gallons of water per 1,000 grains removed. That certificate is the only independent way to identify the most efficient water softener; an Amazon listing that says "high efficiency" without it is a marketing claim. Our cost guide shows how much salt the difference saves.
Small, compact and under-sink water softeners
A compact water softener is usually a cabinet unit with the resin tank inside the salt cabinet, sized at 24,000–32,000 grains for one or two bathrooms; the Kenmore 350 is the compact pick in our rankings. A small water softener still needs the main line, a drain and an outlet, so measure the space and the height under any shelf before you buy. An under sink water softener is a different thing: a point-of-use cartridge or mini tank that treats one tap. It protects a kettle or coffee maker, not the water heater, and most need frequent manual regeneration or cartridge changes. Renters looking for a water softener for apartment use usually can't cut into the main line; the realistic options are a portable softener on a hose connection (see portable and RV softeners) or a filter at one tap, with the landlord's permission for anything plumbed.
Whole house water softener system vs point-of-use
A whole house water softener system protects the water heater, which is where scale costs most money, along with every fixture and appliance. A point-of-use device (a shower filter or under-sink cartridge) treats one tap. For a house, buy whole-house; a whole house water softener is sized by both grains and flow, so check the flow step above as well. Your home water softener system usually goes near the main shut-off, after any well pressure tank and sediment filter, and before the water heater. Leave space above the valve and access to the brine tank lid.
What a soft water system changes day to day
With a soft water system, soap and shampoo lather more, so you use less; spotting on glass and shower doors drops; and white crust stops building on faucets and kettles. The full list is in benefits of a water softener system. Many people notice a slick feel in the shower, which is soap rinsing off differently, not residue. Drinking water gains a little sodium (roughly 8 mg per litre for each gpg removed with sodium salt); if that matters, use potassium chloride or keep one unsoftened tap.
Buying questions, answered
- How do I choose the best water softener for my house?
- Test your hardness, decide between softening (salt) and scale control (salt-free), size it in grains, check the flow rate against your peak use, then pick a valve and layout that fits your space. The 7-step checklist above walks through each.
- How do I size a water softener for my home?
- People × 75 gallons × hardness in gpg (plus about 4 per ppm of iron) × 7 days, plus 25% headroom. The calculator on this page does the maths.
- What grain capacity do I need for a family of 4?
- At 10–12 gpg, about 32,000–40,000 grains; at 20 gpg, about 48,000. Use the calculator with your own hardness.
- What does grain capacity mean on a water softener?
- It's how much hardness the resin removes before it must regenerate, in grains (1 grain = 64.8 mg of calcium carbonate). Makers usually quote it at the maximum salt dose, so real capacity at economical settings is lower.
- What hardness level needs a water softener?
- Above about 7 gpg (120 ppm), the U.S. Geological Survey's 'hard' threshold, most homes benefit. Between 3.5 and 7 gpg it's optional; below 3.5 gpg it isn't needed.
- Do I need a water softener for city water?
- Only if your utility's water is hard. Check its annual water quality report for hardness; many cities supply 5–15 gpg.
- What type of water softener do I need?
- A salt-based softener for soft water and soap savings; a twin-tank model for large or 24/7 households; a salt-free TAC conditioner if you only want less scale and your water is inside its limits.
Where to go from here
On a private well, go to water softeners for well water. If you want filtration as well, see softener and filtration combos. For everything side by side, open the comparison table; quick answers are in the FAQ.