How to read your water test and choose the right system
A lab report or annual water quality report is a page of numbers. Here is what each one actually means, and which category of treatment addresses it, before you buy anything.
Every number on a water test maps to one of a small number of treatment categories, and most of the money wasted on this problem goes toward a system sized against a guess instead of a result. A private well has no federal water-quality regulation at all; the owner is responsible for testing it, choosing what to treat, and confirming the treatment worked. City water is different: a public system already tests continuously and publishes an annual Consumer Confidence Report, so the numbers exist, they are just written for regulators rather than homeowners.
This page is the map from a result to a category of treatment. Two of the categories below have a system on this site; several do not, and this page says so plainly rather than pointing you at something that will not work.
These are the two results this site currently has a system for: hardness, and well-water iron, manganese, or sulfur odor. Read the table below before choosing between them, since several other common results need a different category of system entirely.
| What your test shows | What it means | Category that treats it | On this site |
|---|---|---|---|
| Hardness above 7 gpg | Dissolved calcium and magnesium; scale, soap scum, spotting | Ion-exchange water softener | SS1 softener |
| Iron above 0.3 mg/L | Orange or reddish-brown staining, metallic taste | Oxidizing filter (rated up to 7 PPM on the system below) | WS1 filter |
| Manganese above 0.05 mg/L | Black staining; a health advisory applies above 0.3 mg/L | Oxidizing filter (rated up to 1 PPM on the system below) | WS1 filter |
| Rotten-egg odor | Sulfur bacteria, the water heater, or dissolved hydrogen sulfide gas | Depends on the source; see the dedicated diagnostic below | WS1 filter, for the dissolved-gas case |
| pH below 6.5 | Corrosive water that can leach metal from your own pipes | Acid-neutralizing filter | No system on this site yet |
| Color above 15 units | Tannins from organic matter; tea- or yellow-tinted water | Anion exchange or oxidation, depending on severity | No system on this site yet |
| Arsenic above 10 ppb | An enforceable federal limit tied to cancer and organ risk | Reverse osmosis, activated alumina, or arsenic-rated anion exchange | No system on this site yet |
| Nitrate above 10 mg/L | An enforceable federal limit; infant health risk specifically | Reverse osmosis, nitrate-selective anion exchange, or distillation | No system on this site yet |
| Coliform bacteria present | A pathogen indicator; do not wait to act on this one | UV disinfection, or shock chlorination for a one-time source | No system on this site yet |
| Thresholds are EPA enforceable limits where one exists, EPA secondary (aesthetic) standards where it does not, and manufacturer-rated limits for the specific SpringWell systems named. Full citations are in the sections below. | |||
A single test can and often does return more than one of these at once. Iron and hardness travel together constantly; treat each on its own merits rather than assuming one system covers both.
Start with an actual test, not a guess
If your water comes from a private well, nobody else is testing it. Wells are not covered by the federal Safe Drinking Water Act’s public-system rules, which puts the responsibility for testing, interpreting the result, and confirming treatment worked entirely on the owner. A state-certified laboratory is the right source for a well test; some contaminants, hydrogen sulfide especially, escape from an open container, so use the lab’s own sample bottle and instructions rather than an open jar.
City water works differently. A public water system already tests continuously and is required to publish an annual Consumer Confidence Report (CCR) showing what it found, but that report describes the water leaving the treatment plant, not necessarily what comes out of your specific tap after traveling through the distribution system and your own household plumbing. Reading a CCR is its own skill, and the numbers below apply to it the same way they apply to a private well test, with the caveat that a CCR only covers what the utility is required to test for.
Hardness: the line almost every test has
Hardness is dissolved calcium and magnesium, reported in either milligrams per liter as calcium carbonate or in grains per gallon (gpg), the unit most softener sizing uses. USGS classifies water as soft from 0 to 60 mg/L, moderately hard from 61 to 120, hard from 121 to 180, and very hard above 180, all as calcium carbonate. Converting using the standard factor of 17.1 mg/L per grain, that comes out to roughly soft below 3.5 gpg, moderately hard from 3.5 to 7, hard from 7 to about 10.5, and very hard above that.
Hardness is not a health contaminant; there is no EPA standard for it because it is not regulated as one. What it does is practical and cumulative: scale buildup inside pipes and appliances, reduced soap and detergent effectiveness, and spotting on dishes and fixtures. If your test also shows iron, the two are worth treating as separate line items rather than assuming a softener handles both; our guide to choosing between a softener, a filter, or both works through that decision in full.
Hardness above roughly 7 gpg: SpringWell SS1
Iron and manganese: the two that stain
Iron’s secondary standard is 0.3 mg/L, and manganese’s is a stricter 0.05 mg/L; both are aesthetic thresholds, not enforceable health limits, though manganese carries a separate EPA Health Advisory at 0.3 mg/L for chronic exposure that is worth taking seriously, particularly in a household that mixes infant formula with tap water. Iron produces the familiar orange-to-reddish stain; manganese produces a denser black stain and is easy to mistake for iron until a lab result tells you which one you actually have, or more often, both.
Treatment is chosen by measured concentration. Below about 2 mg/L of dissolved iron, a polyphosphate additive can keep it in suspension rather than removing it, which still leaves a metallic taste. Between roughly 3 and 10 mg/L combined, an oxidizing filter using manganese greensand is the standard whole-house fix. SpringWell’s WS1, the well-water system referenced throughout this site, is manufacturer-rated to 7 PPM iron and 1 PPM manganese, which covers the range most residential wells actually test at; a result meaningfully above either number needs a system rated for it specifically, not this one.
Rotten-egg odor: three different causes, one smell
Hydrogen sulfide odor has its own full diagnostic, because the same smell has three unrelated causes with three different fixes: the water heater’s anode rod, sulfur bacteria in the well or plumbing, or hydrogen sulfide gas actually dissolved in the groundwater. Only the third case is a whole-house filtration problem. The complete breakdown, including how to tell the three apart from your own taps in about five minutes, is in our guide to rotten-egg smell in well water.
pH below 6.5: corrosive water working on your own pipes
The EPA’s secondary standard for pH sets a healthy range of 6.5 to 8.5. Water below that range is acidic and corrosive: rather than affecting the water’s safety at the source, it actively leaches metal, including copper, lead, and zinc, out of your household plumbing and fixtures as it passes through them, on top of a metallic taste and blue-green staining at drains and fixtures. That makes low pH worth acting on even though the standard itself is classified as aesthetic rather than a primary health limit; the mechanism (dissolving metal out of your own pipes) is a real one. The standard fix is a whole-house acid-neutralizing filter using calcite or crushed limestone, sometimes blended with magnesium oxide for very low readings.
Color and tannins: harmless to drink, hard to ignore
Color has its own secondary standard, 15 color units, and organic tannins leaching from decaying vegetation, peat, or wetland-adjacent soil are the usual cause of a tea- or yellow-tinted well. It is an aesthetic issue rather than a recognized health hazard at residential levels. Treatment ranges from anion-exchange resin for lighter tannin loads to oxidation combined with filtration for heavier ones; this site does not yet carry a system built specifically for tannins, so treat this line item as a category to shop for rather than a product to click through from here.
Arsenic and nitrate: the two results that change what happens next
These two are different from everything else on this page. Both carry an enforceable federal Maximum Contaminant Level rather than an aesthetic guideline, which means the EPA has determined a specific health basis for the number. Arsenic’s limit is 10 parts per billion, tied to skin, organ, and cancer risk from chronic exposure. Nitrate’s limit is 10 mg/L measured as nitrogen, tied specifically to methemoglobinemia, or “blue baby syndrome,” in infants under six months old; state health guidance treats even a result above 1 mg/L, well under the enforceable limit, as reason for a household with an infant to test more closely.
Neither an oxidizing filter nor a standard water softener removes arsenic or nitrate. Both need dedicated technology: reverse osmosis, arsenic-rated anion exchange or activated alumina for arsenic, and reverse osmosis, nitrate-selective anion exchange, or distillation for nitrate. This site does not currently carry a system for either, and no page here will tell you otherwise. If your test comes back positive for either one, that is the point to involve a water-treatment professional or your state or county health department directly, particularly with an infant in the house.
Bacteria: the result that means act now, not shop around
Total coliform or E. coli presence on a test is a pathogen indicator, and it is the one result on this page that calls for immediate action rather than research. A licensed well contractor can identify the source; UV disinfection is the standard ongoing safeguard for a well with recurring bacterial presence, and shock chlorination can address a one-time contamination event, though as noted on our hydrogen-sulfide page, it often needs repeating and difficult cases require professional help to do correctly. Until a positive bacterial result is resolved and retested clean, treat the water as unsafe to drink without boiling or an alternative source, and contact your local health department for guidance specific to your situation.
My test shows more than one issue at once. Do I need more than one system?
Often, yes. Hardness and iron are frequently both present and are treated as separate line items rather than assumed to be solved by whichever system you buy first. Read each result against the table above rather than assuming one purchase covers everything your test found.
What is the difference between a secondary standard and an enforceable limit?
An enforceable Maximum Contaminant Level, like the ones for arsenic and nitrate, has a specific health basis and legal force for public water systems. A secondary standard, like the ones for iron, manganese, pH, and color, is aesthetic guidance the EPA does not enforce. Manganese sits in both categories at once: an aesthetic standard at 0.05 mg/L, and a separate, non-enforceable EPA Health Advisory at 0.3 mg/L for chronic health exposure.
How often should I retest my well?
State health guidance commonly recommends annual testing for nitrate and bacteria specifically, since both can change year to year independent of anything else about the well. A full panel less frequently is reasonable once a baseline is established, and always retest after any treatment system is installed to confirm it is actually working at your specific concentration.
My city water report already lists these numbers. Do I still need my own test?
A Consumer Confidence Report describes water as it leaves the treatment plant, not necessarily what reaches your tap after the distribution system and your own household plumbing, which is where issues like lead from old fixtures or pipe corrosion from low pH actually originate. It is a useful starting point, not a replacement for testing your own water if something seems off.
Is a whole-house filter the same thing as a drinking-water filter?
No. A whole-house system like the ones referenced on this page treats water at the point it enters your home, for problems like hardness, iron, manganese, and sulfur odor. Contaminants that need reverse osmosis or a dedicated under-sink system, arsenic and nitrate among them, are typically addressed at the point of use rather than whole-house, which is part of why this site does not point you toward a whole-house system for either one.
Disclosure: this page contains affiliate links, and we may earn a commission if you buy through them, at no extra cost to you. Our recommendations are based on each system’s published specifications and the problem it is built to solve, not on commission. Contaminant figures on this page are sourced to the EPA, USGS, the Minnesota Department of Health, Penn State Extension, and the Water Systems Council.