Salt-free water conditioners: what they do to scale, and what they leave alone
A salt-free conditioner leaves the calcium and magnesium in the water and changes their form, so less of it sticks to hot surfaces as scale. It needs no brine tank or drain. Hardness tests the same before and after, the water does not feel softened, and spots still form on glass. For scale on a water heater and fixtures, on water within the media's limits, that can be enough.
What the research found
Makers lean on two studies. They measured different things, and the makers agree with the second one: US Water Systems says of its own conditioner that "a hardness test reads the same before and after."
Arizona State, 2014
More than 88 percent less scale
In a heated-reservoir test run for the WateReuse Research Foundation, TAC media reduced scale formation by more than 88 percent. Electromagnetic and electrically induced devices came in near 50 percent.
University of Waterloo, 2019
Hardness barely moves
Calcium fell 2.7 to 4.4 percent and magnesium 4.0 to 6.9 percent through TAC media, which the thesis called too small to be of much practical value. The treated water formed somewhat less scale than untreated water.
Quick picks
The short answer for common situations. Each links to the full card below.
A single tank of scale control media with no valve, drain or salt. A. O. Smith says plainly that it does not soften water or remove the minerals that cause hardness; it is meant to cut the scale those minerals leave on heated surfaces.
Flow
7 gpm
Capacity
600,000 gallons or 6 years
Water
Hardness under 15 gpg, iron under 0.3 ppm, pH under 8.3, alkalinity under 250 mg/L
In the box
Tank, shut-off valve, nipple and hose adapter (listing)
Suits: Moderately hard city water under 15 grains per gallon, where scale on the water heater and fixtures is the complaint and no drain is near the main line.
Weigh: Hardness tests the same after it, and there is no softened feel. The water limits are tight: under 15 gpg, iron under 0.3 ppm, pH under 8.3, and A. O. Smith recommends a pre-filter.
TAC media, the type the Arizona State University study tested, in an upflow tank with an in/out head and 1 in elbow adapters. The seller states that it will not soften water or remove the minerals that cause hard water.
Media
TAC, 3 L in an 8 × 35 in tank (seller)
Flow
12 gpm
Capacity
900,000 gallons (listing)
Water
20–120 psi; chlorine under 0.5 ppm, iron under 0.3 ppm, copper under 1.3 ppm, pH 6.5–8.5
Suits: City water that already goes through a carbon filter, where scale is the problem and a drain or salt is out of the question.
Weigh: Chlorine has to be under 0.5 ppm, so on city water it needs carbon in front. The seller's FAQ gives figures (600,000 gallons, 25–80 psi) that conflict with its spec block; the spec block is quoted here.
A tank of Aquasure's anti-scale media behind a sediment, carbon and zinc pre-filter cartridge, sold together. Aquasure's own wording is that it "may not completely remove" hardness; it leaves hardness in the water, as every conditioner here does.
Media
Aquasure anti-scale media, type not named
Pre-filter
Sediment, carbon and zinc cartridge
Flow
Up to 10 gpm (listing)
Capacity
800,000 gallons; 1–3 bathrooms, up to 4 people
Water
Hardness below 25 gpg (listing)
Suits: One to three bathrooms on city water up to 25 gpg, where a pre-filter cartridge in the same install is a plus.
Weigh: Aquasure does not name the media type, and the 25 gpg ceiling and 10 gpm flow come from the listing. The pre-filter cartridge is a recurring cost.
Conditioner media is fussy about the water it sees, and the limits differ by maker:
Hardness ceilings. A. O. Smith under 15 gpg, Aquasure Serene under 25 gpg, SpringWell up to 75 gpg.
Iron and chlorine removed first. Most want iron under 0.3 ppm, so a well with iron needs a softener or iron filter anyway. Tier1 wants chlorine under 0.5 ppm and US Water Systems says it must be removed, so on city water a salt-free install is really carbon plus the conditioner.
Check your utility's numbers on the hardness page before choosing one.
Scale claims, quoted as given
SpringWell says its FutureSoft "prevents up to 95% of scale buildup". Lowe's lists Pentair's NaturSoft as certified for 99.6 percent scale prevention under the German DVGW-W 512 test. The Arizona State figure is more than 88 percent in its own lab protocol. These come from different tests and do not carry from one product to another.
Sold off Amazon
Salt-free conditioners sold elsewhere
Model
Flow
Limits
Where sold
SpringWell FutureSoft FS1, FS4, FS+TAC media with a pre-filter
12, 15 and 20 gpm (the size guide on the same page says 9, 12 and 20)
Up to 75 gpg; no iron or manganese
SpringWell direct
US Water Systems GreenWaveTAC media, 3 to 7 L
10, 15 and 20 gpm
15–100 psi, pH 6.5–8.5, iron under 0.3 mg/L; chlorine removed first
