Reference levels
Every parameter we check, and the exact EPA number your reading is measured against. These are the same published federal standards a public water utility has to meet. Private wells aren't required to.
| Parameter | Level | Type | Category |
|---|---|---|---|
| Nitrate (as N) The most common well-water contaminant tied to septic systems, fertilizer, and livestock runoff. The MCL exists specifically to prevent methemoglobinemia ("blue baby syndrome") in infants; wells that feed infant formula deserve extra caution even below the limit. | 10 mg/L | EPA Maximum Contaminant Level | Health-based |
| Nitrite (as N) Related to nitrate; usually a marker of very recent contamination since nitrite converts to nitrate quickly. | 1 mg/L | EPA Maximum Contaminant Level | Health-based |
| Arsenic Naturally occurring from bedrock geology in parts of the country (notably New England, the upper Midwest, and parts of the Southwest); doesn't change taste, smell, or color, which is why testing is the only way to know. | 10 µg/L | EPA Maximum Contaminant Level | Health-based |
| Lead Almost always a plumbing problem (lead solder, brass fixtures, service lines) rather than the aquifer itself. A first-draw sample after standing water is the standard way to catch it. 15 µg/L is the Lead and Copper Rule action level, the standard reference point since no exposure level for lead is fully safe. | 15 µg/L | EPA Lead and Copper Rule action level | Health-based |
| Copper Usually leaches from copper plumbing, especially in acidic water. Metallic taste and blue-green staining are common tells. | 1.3 mg/L | EPA Lead and Copper Rule action level | Health-based |
| Total Coliform A screening indicator, not itself usually harmful. Presence means surface water or soil organisms are getting into the well, which is the problem worth chasing down: well cap, casing, nearby septic. | Presence/absence | EPA Maximum Contaminant Level | Health-based |
| E. coli A direct fecal-contamination indicator. Any detection is a do-not-drink-until-resolved result, not a borderline one. | Presence/absence | EPA Maximum Contaminant Level | Health-based |
| Fluoride Naturally occurring in groundwater in some regions. The 4.0 mg/L MCL guards against skeletal fluorosis; EPA's lower 2.0 mg/L secondary standard exists to prevent cosmetic dental fluorosis in children. | 4 mg/L | EPA Maximum Contaminant Level | Health-based |
| Uranium Naturally occurring, tied to local bedrock (granite, phosphate deposits). More common in parts of the West and Southwest. | 30 µg/L | EPA Maximum Contaminant Level | Health-based |
| Combined Radium (226/228) A naturally occurring radionuclide from bedrock. Reported as combined Radium-226 and Radium-228. | 5 pCi/L | EPA Maximum Contaminant Level | Health-based |
| Gross Alpha (excl. radon/uranium) A screening measure for radioactive alpha-emitters as a group; a high reading usually prompts testing for the specific radionuclide. | 15 pCi/L | EPA Maximum Contaminant Level | Health-based |
| Manganese No enforceable federal MCL, but EPA's health advisory is 300 µg/L (lifetime), well above the much lower 50 µg/L secondary standard set for staining and taste. A result can look fine on taste alone and still be worth a second look for infant formula use. | 300 µg/L | EPA Health Advisory (no enforceable MCL exists) | Health-based |
| Iron A taste/staining standard, not a health limit. Reddish-brown staining and metallic taste above this level are common and harmless to drink. | 0.3 mg/L | EPA Secondary Standard (taste/odor, not health-based) | Aesthetic (taste/odor) |
| Sulfate A taste standard ("rotten egg" or bitter taste, laxative effect at high levels), not a health limit. | 250 mg/L | EPA Secondary Standard (taste/odor, not health-based) | Aesthetic (taste/odor) |
| Chloride A taste standard, often elevated by road salt runoff or saltwater intrusion in coastal wells, not a health limit. | 250 mg/L | EPA Secondary Standard (taste/odor, not health-based) | Aesthetic (taste/odor) |
| Total Dissolved Solids (TDS) A general mineral-content measure: a taste and scaling standard, not a health limit on its own. | 500 mg/L | EPA Secondary Standard (taste/odor, not health-based) | Aesthetic (taste/odor) |
| Hardness (as CaCO3) No EPA standard at all. Reported for context. Above roughly 180 mg/L is generally considered "very hard," mainly a plumbing and appliance-scaling nuisance. | No numeric limit | EPA Secondary Standard (taste/odor, not health-based) | Aesthetic (taste/odor) |
| pH EPA's secondary range is 6.5-8.5. Outside that range is mainly a corrosivity/plumbing concern (acidic water can leach lead and copper from pipes) rather than a direct health limit. | No numeric limit | EPA Secondary Standard (taste/odor, not health-based) | Aesthetic (taste/odor) |
| Radon EPA has proposed, but never finalized, a waterborne radon standard: 4,000 pCi/L if a state has an indoor-air radon program, 300 pCi/L otherwise. Shown here at the higher, more common reference point. Check with your state health department for which one applies. More common in wells drilled into granite bedrock. | 4000 pCi/L | EPA Health Advisory (no enforceable MCL exists) | Health-based |
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