What your well water results mean
Got a lab report back? Here's what the most common numbers mean, how they compare to EPA and Health Canada reference values, and what to do next. This is not medical advice.
Reference values verified 2026-10-27 against EPA primary/secondary standards and Health Canada Guidelines for Canadian Drinking Water Quality summary tables.
Quick reference
| Parameter | EPA (US) | Health Canada | Health vs nuisance |
|---|---|---|---|
| Total coliform & E. coli | E. coli MCL is a treatment technique goal of zero (none present). A positive tot… | E. coli MAC: none detectable per 100 mL. Total coliforms are used as an operatio… | Health risk when E. coli (or enterococci) is present. Total |
| Nitrate / nitrite | Nitrate MCL 10 mg/L as nitrogen. Nitrite MCL 1 mg/L as nitrogen. | Nitrate MAC 10 mg/L as nitrate-nitrogen (45 mg/L as nitrate). Nitrite MAC 1 mg/L… | Health — especially infants under 6 months and pregnant peop |
| Iron | Secondary MCL (SMCL) 0.3 mg/L (aesthetic). | Aesthetic objective (AO) 0.3 mg/L. | Mostly nuisance (stains, taste). Very high levels can affect |
| Manganese | SMCL 0.05 mg/L (aesthetic). EPA has also issued a health advisory for bottle-fed… | MAC 0.12 mg/L; AO 0.02 mg/L. | Both — stains at low levels; health MAC protects bottle-fed |
| Hardness (calcium & magnesium) | No MCL. Often expressed as mg/L as CaCO3; 'hard' water commonly starts around 12… | No health-based MAC; aesthetic/operational issue. | Nuisance / plumbing — not usually a health MCL issue. |
| pH | SMCL range typically 6.5–8.5. | Aesthetic objective generally 7.0–10.5 for treated distribution systems; private… | Indirect health risk via metals (lead/copper) when corrosive |
| Sulfate / hydrogen sulfide | Sulfate SMCL 250 mg/L. No federal MCL for H2S (odor-driven). | Sulfate AO 500 mg/L. H2S is primarily an aesthetic/odor issue. | Mostly nuisance (taste/odor, laxative effect at high sulfate |
| Arsenic | MCL 0.010 mg/L (10 µg/L). | MAC 0.010 mg/L (10 µg/L). | Health — chronic risk. Not a nuisance parameter. |
| Lead / copper | Lead action level 0.015 mg/L (15 µg/L) in public systems under the Lead and Copp… | Lead MAC 0.005 mg/L (5 µg/L). Copper AO 1.0 mg/L. | Lead is a serious health risk (especially children). Copper |
| Total dissolved solids (TDS) | SMCL 500 mg/L. | AO 500 mg/L. | Mostly aesthetic; investigate which ions make up the TDS. |
| Fluoride | MCL 4.0 mg/L; SMCL 2.0 mg/L. | MAC 1.5 mg/L. | Health at high levels; staining of teeth is an early sign in |
| Uranium / radon | Uranium MCL 0.030 mg/L (30 µg/L). No federal MCL for radon in drinking water for… | Uranium MAC 0.02 mg/L (20 µg/L). Radon is addressed mainly via indoor-air guidan… | Health (kidney risk for uranium; lung cancer risk pathway fo |
| Chloride / sodium | Chloride SMCL 250 mg/L. Sodium has a drinking-water advisory for people on very … | Chloride AO 250 mg/L. Sodium AO 200 mg/L. | Mostly taste/corrosion; sodium matters for some medical diet |
Total coliform & E. coli
What it means: Coliform bacteria are indicators. Total coliforms can come from the environment; E. coli points to fecal contamination and a higher chance of pathogens.
EPA: E. coli MCL is a treatment technique goal of zero (none present). A positive total-coliform or E. coli result on a private well means do not drink untreated water until you retest and fix the cause.
Health Canada: E. coli MAC: none detectable per 100 mL. Total coliforms are used as an operational/indicator parameter; detection warrants investigation.
Health vs. nuisance: Health risk when E. coli (or enterococci) is present. Total coliform alone is a warning about well integrity, not always an immediate illness signal.
What to do: Stop drinking the water (use bottled or boiled water for drinking/cooking if advice says boil works for bacteria). Shock-chlorinate the well after fixing sanitary defects, then retest with a certified lab (often 1 week and again ~4 weeks later). Call your health department if E. coli is confirmed.
Nitrate / nitrite
What it means: Forms of nitrogen from fertilizer, manure, septic systems, and natural soil processes. Dangerous for infants (methemoglobinemia / 'blue baby' risk).
EPA: Nitrate MCL 10 mg/L as nitrogen. Nitrite MCL 1 mg/L as nitrogen.
Health Canada: Nitrate MAC 10 mg/L as nitrate-nitrogen (45 mg/L as nitrate). Nitrite MAC 1 mg/L as nitrite-nitrogen.
Health vs. nuisance: Health — especially infants under 6 months and pregnant people. No reliable taste/smell warning.
What to do: Do not boil (boiling concentrates nitrate). Use bottled water for infant formula if above the standard. Retest to confirm. Treatment options include anion exchange, reverse osmosis, or distillation at the tap — choose NSF/ANSI-certified gear for nitrate reduction and retest after install.
Iron
What it means: Common in groundwater. Causes rusty stains, metallic taste, and orange water.
EPA: Secondary MCL (SMCL) 0.3 mg/L (aesthetic).
Health Canada: Aesthetic objective (AO) 0.3 mg/L.
Health vs. nuisance: Mostly nuisance (stains, taste). Very high levels can affect plumbing and appliances.
What to do: Confirm with a lab (dissolved vs. total iron matters). Treatment often includes oxidation + filtration, water softeners for low ferrous iron, or specialized iron filters. Retest after treatment.
Manganese
What it means: Natural mineral. Black/brown stains, bitter taste; also a health concern for infants at higher levels.
EPA: SMCL 0.05 mg/L (aesthetic). EPA has also issued a health advisory for bottle-fed infants.
Health Canada: MAC 0.12 mg/L; AO 0.02 mg/L.
Health vs. nuisance: Both — stains at low levels; health MAC protects bottle-fed infants.
What to do: Use another water source for infant formula if above health guidance. Treatment: oxidation/filtration, water softener (limited), or RO for drinking water. Retest after install.
Hardness (calcium & magnesium)
What it means: Dissolved calcium and magnesium. Causes scale, soap scum, and dry skin/hair complaints.
EPA: No MCL. Often expressed as mg/L as CaCO3; 'hard' water commonly starts around 120 mg/L.
Health Canada: No health-based MAC; aesthetic/operational issue.
Health vs. nuisance: Nuisance / plumbing — not usually a health MCL issue.
What to do: Water softener (ion exchange) is the usual whole-house fix. Keep a separate unsoftened tap for drinking if you prefer, and maintain salt/resin as directed.
pH
What it means: How acidic or basic the water is. Low pH can corrode pipes and pull metals into water; high pH can cause scale and taste issues.
EPA: SMCL range typically 6.5–8.5.
Health Canada: Aesthetic objective generally 7.0–10.5 for treated distribution systems; private wells still use pH as a corrosion/operational clue.
Health vs. nuisance: Indirect health risk via metals (lead/copper) when corrosive.
What to do: If pH is low and metals are high, fix corrosion (neutralizing filter, etc.) and retest lead/copper. Work with a treatment pro and a certified lab.
Sulfate / hydrogen sulfide
What it means: Sulfate is a dissolved mineral; hydrogen sulfide (H2S) is the 'rotten egg' gas from bacteria or reactions in the well/plumbing.
EPA: Sulfate SMCL 250 mg/L. No federal MCL for H2S (odor-driven).
Health Canada: Sulfate AO 500 mg/L. H2S is primarily an aesthetic/odor issue.
Health vs. nuisance: Mostly nuisance (taste/odor, laxative effect at high sulfate). Investigate bacterial sulfate reduction if odor is strong.
What to do: For H2S: shock chlorination, aeration, oxidizing filters, or activated carbon depending on level. For high sulfate: RO or anion exchange for drinking water. Retest after treatment.
Arsenic
What it means: Naturally occurring in some bedrock aquifers. No taste or smell. Long-term exposure raises cancer and other health risks.
EPA: MCL 0.010 mg/L (10 µg/L).
Health Canada: MAC 0.010 mg/L (10 µg/L).
Health vs. nuisance: Health — chronic risk. Not a nuisance parameter.
What to do: Do not boil. Use bottled water for drinking/cooking until treated. Point-of-use RO, adsorptive media, or anion exchange systems certified for arsenic reduction; retest treated water yearly.
Lead / copper
What it means: Usually from plumbing, pumps, or fixtures — especially with corrosive water — not from the aquifer itself.
EPA: Lead action level 0.015 mg/L (15 µg/L) in public systems under the Lead and Copper Rule; goal is zero. Copper action level 1.3 mg/L.
Health Canada: Lead MAC 0.005 mg/L (5 µg/L). Copper AO 1.0 mg/L.
Health vs. nuisance: Lead is a serious health risk (especially children). Copper can cause stomach upset and blue-green stains.
What to do: Use a first-draw sample as the lab instructs. Flush taps before drinking if advised. Replace leaded components; consider certified NSF/ANSI 53 filters for lead. Fix corrosive pH. Retest after changes.
Total dissolved solids (TDS)
What it means: Sum of dissolved minerals. High TDS tastes salty or mineral-heavy and can stress plumbing and treatment gear.
EPA: SMCL 500 mg/L.
Health Canada: AO 500 mg/L.
Health vs. nuisance: Mostly aesthetic; investigate which ions make up the TDS.
What to do: Look at the full panel (sodium, chloride, hardness, sulfate). RO reduces TDS at the tap. Softening alone does not remove all TDS.
Fluoride
What it means: Can be natural in groundwater. Protects teeth at low levels; excess risks dental/skeletal fluorosis.
EPA: MCL 4.0 mg/L; SMCL 2.0 mg/L.
Health Canada: MAC 1.5 mg/L.
Health vs. nuisance: Health at high levels; staining of teeth is an early sign in children.
What to do: If above guidance, use an alternate drinking source for kids and consider RO or activated alumina systems rated for fluoride. Retest yearly if treating.
Uranium / radon
What it means: Naturally occurring radioactive elements in some bedrock. Uranium is a dissolved metal; radon is a gas that can move from water into indoor air when taps run.
EPA: Uranium MCL 0.030 mg/L (30 µg/L). No federal MCL for radon in drinking water for private wells; EPA has proposed/guidance levels historically discussed around 300–4,000 pCi/L depending on context — confirm with your state lab and health department.
Health Canada: Uranium MAC 0.02 mg/L (20 µg/L). Radon is addressed mainly via indoor-air guidance; ask provincial labs about water radon testing where available.
Health vs. nuisance: Health (kidney risk for uranium; lung cancer risk pathway for radon via air).
What to do: Test with an accredited lab experienced in radionuclides. Uranium: RO or anion exchange. Radon in water: aeration treatment; also test indoor air. Do not rely on boiling.
Chloride / sodium
What it means: Salt-related ions from road salt, water softeners, seawater intrusion, or geology. Taste and corrosion clues.
EPA: Chloride SMCL 250 mg/L. Sodium has a drinking-water advisory for people on very low-sodium diets (often discussed near 20 mg/L for that population) — not a formal MCL.
Health Canada: Chloride AO 250 mg/L. Sodium AO 200 mg/L.
Health vs. nuisance: Mostly taste/corrosion; sodium matters for some medical diets.
What to do: If you soften water, keep a hard-water tap for drinking/cooking. RO reduces sodium/chloride at the tap. Investigate softener settings and nearby salt sources. People on sodium-restricted diets should ask their clinician.
Disclaimer: This page is educational, not medical or legal advice. Lab methods and units vary. Compare your report to the numbers printed on it, and ask a certified/accredited lab or your local health department before changing treatment or drinking habits. If someone is ill, contact a clinician.