The specs an owner actually needs.
Independent, numbers-first answers about the equipment in your home: what the spec actually means, what size you need, and which part fits.
Short answer
21,000 grainsA four-person household on 10 gpg water, regenerating every 7 days, needs 21,000 grains of softener capacity between regenerations. Nearest nominal size: 24,000 grains.
Diagnostic guides: a symptom or a lab result in, a treatment class out, with the EPA or NSF limit cited by number.
8 guides
Sizing calculators for home water treatment: grain capacity, flow rate, micron rating and more, with the formula shown.
2 calculators
Model number to replacement part: which cartridge, membrane or lamp fits, on what interval, and which cross-fit alternatives exist.
2 parts
System comparisons segmented by the problem being solved, chosen against a stated method from published specifications.
2 reviews
Latest pages
All guides
Compare
Best iron filter for well water: air injection vs manganese greensand vs Birm, by published spec
Iron plus manganese 3 to 10 mg/L: an AIO such as the AFW AIS10-25SXT (10 ppm iron) or Birm at pH 6.8 to 9.0. Under 3.0 ppm with no drain line: the iSpring WGB32BM.
Compare
Best whole-house sediment filter for well water: spin-down vs cartridge, by published spec
Coarse sand: a Rusco spin-down, 1 to 25 GPM, screens 700 to 15 micron. Fine silt: a Pentek 150233 Big Blue at 1 psi @ 15 gpm with a 5 micron nominal cartridge.
Diagnose
Black stains from well water: how much manganese that is and what removes it
Black stains on a private well mean manganese above EPA's secondary standard of 0.05 mg/L. Why it resists iron treatment, and which class fits each mg/L range.
Diagnose
Blue-green stains and pinhole leaks: low pH well water and what neutralizes it
Blue-green stains on a well are copper dissolved by low-pH water. EPA's pH range is 6.5 to 8.5; an acid-neutralizing filter treats down to pH 5.3.
Match
Express Water WH300SCKS Replacement Filters: Which Cartridges Fit, and Cross-Fit Alternatives
Express Water WH300SCKS takes FLTWH2045S1, FLTWH2045K and FLTWH2045C1 (set FLTWH2045CKS1), 4.5 x 20 in, changed every 6-12 months or 100,000 gallons.
Diagnose
How to shock chlorinate a well: chlorine amount, contact time, and when it is the wrong fix
Shock chlorinate a well at 50 to 200 ppm with plain 6% or 8.25% bleach, hold it 2 to 6 hours or overnight, flush to 0 ppm, retest in 2 to 4 weeks.
Why the numbers here check out
Most equipment questions have one correct answer and it is a number. How many grains of capacity for four people on 22 gpg water. What micron rating a sediment filter needs on a well. Which cartridge fits a housing you already own.
Those answers are usually published by whoever wants to sell you the hardware. OwnerSpec publishes them independently: the formula, the inputs, the working, and the source it came from, so you can check it rather than trust it.
Independent
No manufacturer, dealer or installer owns a number on this site. Affiliate links are disclosed on every page that carries one.
Cited to the source
Limits come from EPA, NSF/ANSI and extension services by number. Capacities and part numbers come from the manufacturer's own manual or data sheet.
Dated
Every page shows when its facts were last verified and last updated, so you know how old the number is before you use it.