Home water treatment
Test the water first, then size the equipment
Quick answer
16 calculators and 345 computed reference pages for softener sizing, salt and regeneration, whole house flow rate, filter life, reverse osmosis output and ultraviolet dose. Every figure is labeled as a published standard, a rule of thumb, or something that only comes off your own water test, because on this subject those three are not the same thing.
Start with a number you do not have yet
- Water Softener Sizing Calculator The grain capacity your house actually needs, from your measured hardness and household size, with the nameplate size that lands on. The number on the box is the capacity at maximum salt dose, not a working figure.
- Water Hardness Converter Grains per gallon to milligrams per liter and back, at the published conversion of 17.1, with the USGS classification your result falls into. Laboratories report in ppm and equipment is sized in grains, which is where most of the confusion starts.
- Daily Hardness Load Calculator How many grains of hardness your household removes every day, including the compensation for dissolved iron and manganese that a softener also exchanges. This is the figure every other softener answer is built on.
- Water Softener Salt Calculator Salt per regeneration, per year, and what it costs, at your chosen salt setting. The efficient setting uses less than half the salt for about two thirds of the capacity, which is the trade nobody explains at the point of sale.
- Regeneration Frequency Calculator Days between regenerations for your size, hardness and household, against the three to fourteen day window that keeps a resin bed healthy without wasting salt.
- Resin Volume Calculator The resin volume behind any nameplate rating, and what that volume genuinely delivers at each salt dose, from the published resin exchange capacity curve.
Two complete ladders, because there are two kinds of water
A city customer has a utility that treats water to a regulated standard and publishes a report every year at no charge. A well owner has no utility, no report and no operator, and nobody tests the water but them. Pushing both through one ladder would give bad advice to both, so there are two.
City water
Well water
Look up a computed answer
- Water Softener Size by Hardness and Household The grain capacity a household actually needs at every hardness from 3 to 50 grains per gallon, with the daily hardness load, the regeneration interval and the annual salt cost behind each answer. 72 pages
- Regeneration Frequency and Salt Use by Softener Size How often each nameplate size regenerates at every hardness, what each salt setting costs in efficiency, and what actually happens during a regeneration cycle. 42 pages
- Whole House Flow Rate by Bathrooms and Occupants The peak gallons per minute a house has to pass, which is what decides the filter housing size. Fixture flow rates are federal maximums; the bathroom count method is trade convention. 35 pages
- Filter Cartridge Life by Rated Gallons and Household Use How long a rated cartridge lasts at each level of household use, why the rating is an upper bound rather than a schedule, and why pressure drop is the only trigger worth acting on. 36 pages
- Reverse Osmosis Output and Drain Ratio by Membrane and Pressure What a rated membrane actually produces at household feed pressure and temperature, rather than at the 60 psi and 77 degree laboratory test conditions, plus the gallons to drain per gallon made. 30 pages
- Ultraviolet Dose Delivered at Every Flow Rate The dose an ultraviolet system actually delivers as flow rises, against the NSF/ANSI 55 Class A figure of 40 mJ/cm2 and the Class B figure of 16, plus the water clarity it needs to work at all. 40 pages
- What Every Water Hardness Level Means Every hardness from 1 to 50 grains per gallon in both grains and milligrams per liter, its USGS classification, what it does to appliances, and the softener size it points at. 35 pages
- Iron Treatment by Measured Level and Form What each measured iron level needs, split by the three forms that need three different machines: clear water iron, red water iron and iron bacteria. 27 pages
- Sediment Micron Selection by Water Source Which micron rating belongs where, staged coarse to fine by water source, and the nominal against absolute distinction that decides whether a rating means anything. 28 pages
Three kinds of number, labeled separately
The grains per gallon to milligrams per liter conversion of 17.1. The USGS hardness classification. Resin exchange capacity at a stated salt dose. The NSF/ANSI standard numbers and what each one covers. EPA maximum contaminant levels and secondary standards. Federal maximum fixture flow rates. The NSF/ANSI 55 ultraviolet dose classes. These do not move because somebody disagrees with them.
Eighty gallons per person per day as a sizing figure. Regenerating about once a week. Adding three to five grains of compensated hardness per part per million of dissolved iron. Sizing a whole house filter by bathroom count. All taught everywhere, all useful for planning, and none of them published by any standards body.
Hardness, iron, manganese, pH, total dissolved solids, nitrate, bacteria. Nothing on this site supplies one of these and nothing here can override one. This is the pill that matters most, because sizing equipment for a number nobody measured is the most expensive mistake in the category.
There is a fourth category we handle by refusing to fill it in. Where no published figure exists, we say so. There is no EPA limit for hardness of any kind, because hardness is not a health contaminant. We publish no generic water volume per regeneration, because it is set by the control valve program and varies by more than a factor of two between units with the same nameplate. We publish no generic pressure drop, because every cartridge has its own published curve. A blank that says "not published" is a better answer than a number nobody can stand behind.
What is on the site
| Section | Pages | What it is |
|---|---|---|
| Calculators | 16 | Every one shows its formula and labels the basis of every figure it prints. |
| Computed reference | 345 | Nine clusters generated from the same formulas the calculators use. |
| Spec sheets | 49 | Every figure each manufacturer publishes, with nothing estimated. |
| Guides, roundups and charts | 130 | Researched from published standards and owner-review consensus. |
| Complete systems | 6 | Two ladders of three tiers, every item priced and linked, in plumbing order. |
| Verified products | 191 | Every ASIN resolved live and every returned title read against the product claimed. |
The safety part, which is not the fine print
Nothing here diagnoses your water or says a product makes it safe to drink. That is a laboratory result, not a property of a product. What this site does is describe what a contaminant is, what the published standard says about it, and what class of equipment is designed to address it.
Bacteria, nitrate, lead, arsenic and PFAS are not do it yourself topics. They are invisible and tasteless, so nothing tells you whether equipment has stopped working. The limits are legal figures rather than preferences, and lead does not even have a maximum contaminant level: it has an action level of 0.015 mg/L, which is a trigger for utility action rather than a safe concentration, and the health goal is zero. No filter pitcher addresses any of them. Talk to your local health department or a licensed water treatment professional first.
A certification covers a specific claim, not the whole unit. NSF/ANSI 42 is aesthetic effects such as chlorine taste and odor, and it is not a lead claim. 53 is health effects, claim by claim. 44 is softeners. 55 is ultraviolet, where Class A delivers 40 mJ/cm2 for water not known to be safe and Class B delivers only 16 as a supplement to water already considered safe. 58 is reverse osmosis. 372 is the lead content of a fitting rather than lead removal. The phrase "NSF certified" with no number attached tells you very little, and saying so is one of the more useful things this site does.
Get the water tested before you spend anything. On city water the Consumer Confidence Report your utility publishes every year is free and covers the regulated contaminants. On a private well only a certified laboratory test tells you what you have. Hardness is the one figure you can genuinely read at home in under a minute with a strip, so there is no reason to guess at it.
Get the complete water treatment shopping list
Every item in the starter, complete and premium systems for both city water and well water, with running totals, in one printable list. It opens with the test kit, because that is genuinely the first purchase. No charge.
One list, no sequence of daily emails, and you can leave at any time.