Well Water Glossary

Iron

A naturally occurring mineral found in groundwater. Iron causes orange/rust staining on fixtures and laundry and gives water a metallic taste.

EPA Secondary MCL: 0.3 mg/L (ppm)

Manganese

A mineral that causes black or brown staining and can affect the taste of water. Often found alongside iron in well water.

EPA Secondary MCL: 0.05 mg/L (ppm). EPA Health Advisory: 0.3 mg/L

Arsenic

A toxic element found naturally in bedrock that dissolves into groundwater. Odorless and tasteless, making testing the only way to detect it.

EPA MCL: 10 ppb (0.01 mg/L)

Nitrates

Compounds that enter groundwater from fertilizers, septic systems, and animal waste. Especially dangerous for infants under 6 months (blue baby syndrome).

EPA MCL: 10 mg/L (ppm)

Coliform Bacteria

A group of bacteria used as indicators of potential contamination. Total coliform presence suggests a pathway for pathogens to enter your well.

EPA MCL: 0 (no coliform should be present)

E. coli

A specific type of coliform bacteria that indicates fecal contamination. Its presence in well water is a serious health concern requiring immediate action.

EPA MCL: 0 (any detection requires action)

Hydrogen Sulfide

A gas dissolved in groundwater that produces a rotten egg smell. Created by sulfur-reducing bacteria or naturally occurring sulfur deposits in bedrock.

No EPA standard. Nuisance threshold: 0.05 mg/L (detectable by smell)

Fluoride

A naturally occurring mineral in groundwater. While small amounts support dental health, excessive levels can cause dental and skeletal fluorosis.

EPA MCL: 4.0 mg/L. EPA Secondary MCL: 2.0 mg/L

Lead

A toxic metal that typically enters water from corroded plumbing, solder, or fixtures rather than the well itself. No safe level of lead exposure.

EPA Action Level: 15 ppb (0.015 mg/L)

Radon

A radioactive gas that dissolves into groundwater from natural uranium decay in rock. Released into indoor air during showering and other water use.

EPA proposed MCL: 300 pCi/L (not yet finalized)

Uranium

A radioactive element found naturally in certain rock formations. Long-term exposure through drinking water can damage kidneys.

EPA MCL: 30 µg/L (ppb)

VOCs (Volatile Organic Compounds)

Chemical compounds from industrial solvents, gasoline, and pesticides that can contaminate groundwater. Many are known carcinogens.

Varies by compound. EPA regulates 21 specific VOCs with individual MCLs.

PFAS (Per- and Polyfluoroalkyl Substances)

Synthetic chemicals used in nonstick coatings, firefighting foam, and food packaging. Known as 'forever chemicals' because they do not break down in the environment.

EPA MCL (2024): 4 ppt for PFOA and PFOS individually

Tannins

Organic compounds from decaying vegetation that give water a yellow or tea-like color. Common in shallow wells near wetlands or forested areas.

No EPA standard. Aesthetic issue affecting color and taste.

Sediment

Particles of sand, silt, clay, or rust suspended in water. Can clog fixtures and damage appliances. Often indicates well casing or screen issues.

No EPA standard. Measured by turbidity (NTU).

Turbidity

A measure of water cloudiness caused by suspended particles. High turbidity can harbor bacteria and indicates possible contamination pathways.

EPA standard for public systems: 1 NTU (max), 0.3 NTU (95th percentile)

Hardness (Calcium Carbonate)

The concentration of dissolved calcium and magnesium in water. Hard water causes scale buildup in pipes, water heaters, and fixtures.

No EPA standard. Soft: <1 gpg. Moderate: 1-7 gpg. Hard: 7-10.5 gpg. Very Hard: >10.5 gpg.

TDS (Total Dissolved Solids)

The total amount of dissolved minerals, salts, and metals in water. A general indicator of water quality, though not all dissolved solids are harmful.

EPA Secondary MCL: 500 mg/L

Chloride

A naturally occurring ion that can indicate road salt contamination or seawater intrusion. High levels give water a salty taste and corrode pipes.

EPA Secondary MCL: 250 mg/L

Copper

A metal that leaches into water from corroded copper pipes, especially in acidic (low pH) water. Causes blue-green stains on fixtures.

EPA Action Level: 1.3 mg/L

PPM (Parts Per Million)

A unit of concentration equivalent to milligrams per liter (mg/L). Used for most common contaminants like iron, manganese, and nitrates.

PPB (Parts Per Billion)

A unit of concentration equivalent to micrograms per liter (µg/L). Used for trace contaminants like arsenic, lead, and PFAS where even tiny amounts matter.

mg/L (Milligrams Per Liter)

The standard unit for measuring contaminant concentration in water. Equivalent to parts per million (ppm). Most water test results report in mg/L.

GPG (Grains Per Gallon)

A unit used specifically for water hardness. 1 gpg = 17.1 mg/L of calcium carbonate. Water softeners are sized based on gpg.

MCL (Maximum Contaminant Level)

The highest level of a contaminant allowed in public drinking water, set by the EPA. Private wells are not regulated by MCLs, but they serve as the best available safety benchmarks.

SMCL (Secondary Maximum Contaminant Level)

EPA guidelines for contaminants that affect taste, odor, or appearance but are not considered health hazards. Includes iron, manganese, and TDS.

Action Level

The concentration of a contaminant that triggers required treatment or notification. Used for lead (15 ppb) and copper (1.3 mg/L) instead of MCLs.

Detection Limit

The lowest concentration a lab can reliably measure. Results below the detection limit are reported as 'ND' (not detected) or '<DL'.

Air Injection Oxidation

A chemical-free treatment method that injects air into water to oxidize dissolved iron, manganese, and hydrogen sulfide into solid particles that are then filtered out.

Catalytic Carbon

A specialized activated carbon filter media that removes hydrogen sulfide, iron, and chlorine through catalytic reaction rather than simple adsorption. Effective for iron under 3 ppm.

Greensand

A naturally mined mineral filter media (glauconite) coated with manganese oxide. Oxidizes and filters iron, manganese, and hydrogen sulfide. Requires periodic regeneration with potassium permanganate.

KDF (Kinetic Degradation Fluxion)

A copper-zinc alloy filter media that removes chlorine, heavy metals, and controls bacteria through electrochemical oxidation-reduction. Often used as a pre-filter stage.

Ion Exchange

A treatment process where unwanted ions (calcium, magnesium, iron) are swapped for sodium or potassium ions as water passes through a resin bed. The principle behind water softeners.

Reverse Osmosis (RO)

A treatment method that forces water through a semipermeable membrane, removing up to 99% of dissolved contaminants including arsenic, lead, fluoride, nitrates, and PFAS.

UV Disinfection

A chemical-free method that uses ultraviolet light to destroy bacteria, viruses, and other microorganisms by damaging their DNA. Does not change water taste or chemistry.

Chemical Injection

A treatment method that uses a pump to inject chlorine or hydrogen peroxide into water before filtration. Used for high levels of iron (>7 ppm), manganese, or bacteria.

Acid Neutralizer

A tank-based system filled with calcite or corosex media that raises the pH of acidic well water. Prevents blue-green stains from copper corrosion and protects plumbing.

Water Softener

A system that uses ion exchange resin to remove calcium and magnesium (hardness minerals) from water. Prevents scale buildup in pipes, water heaters, and appliances.

Sediment Filter

A pre-filter that removes sand, silt, rust, and other particles from water. Rated in microns — 5 micron is standard for well water. Protects downstream treatment equipment.

Activated Alumina

A porous aluminum oxide filter media highly effective at removing fluoride and arsenic from water through adsorption. Requires periodic media replacement.