Water Quality Glossary

PPM (Parts Per Million)

A measurement unit for water hardness and dissolved solids. 1 PPM equals 1 milligram per liter (mg/L). Water with hardness above 120 PPM is generally considered hard enough to benefit from treatment.

GPG (Grains Per Gallon)

An alternative unit for water hardness used by the water softener industry. 1 GPG equals 17.1 PPM. Most softener manufacturers recommend treatment above 7 GPG.

PFAS (Per- and Polyfluoroalkyl Substances)

A group of over 12,000 synthetic chemicals known as "forever chemicals" because they do not break down in the environment. The EPA set a maximum contaminant level of 4 parts per trillion (ppt) for individual PFAS compounds in drinking water in 2024.

TDS (Total Dissolved Solids)

A measure of all dissolved minerals, salts, metals, and organic material in water, measured in PPM. The EPA secondary standard recommends TDS below 500 PPM for taste and aesthetic reasons.

MCL (Maximum Contaminant Level)

The highest level of a contaminant legally allowed in public drinking water, as set by the EPA under the Safe Drinking Water Act. MCLs are enforceable federal standards.

CCR (Consumer Confidence Report)

An annual water quality report that public water systems are required to provide to customers. It includes testing results for regulated contaminants, the source of your water, and any violations.

Ion Exchange

The process used by salt-based water softeners to remove hardness minerals. Hard water passes through a resin bed that swaps calcium and magnesium ions for sodium ions. The resin is periodically regenerated with salt brine.

Reverse Osmosis (RO)

A water purification process that forces water through a semipermeable membrane, removing 95-99% of dissolved solids including PFAS, lead, nitrates, and hardness minerals. Typically installed as a point-of-use system under the kitchen sink.

GAC (Granular Activated Carbon)

A filtration medium made from carbon-rich materials like coconut shell or coal. GAC filters remove chlorine, some PFAS, volatile organic compounds (VOCs), and taste and odor compounds through adsorption.

Catalytic Carbon

A specialized form of activated carbon that has been treated to enhance its ability to remove chloramine, hydrogen sulfide, and iron. Required in cities that use chloramine instead of chlorine for disinfection.

Scale

The white, chalky mineral buildup that forms when hard water is heated or evaporates. Composed primarily of calcium carbonate (CaCO₃). Scale reduces water heater efficiency, restricts pipe flow, and damages appliances.

Grain Capacity

A rating used for water softeners that indicates how many grains of hardness the system can remove before needing to regenerate. A 48,000-grain softener serving a family of four with 25 GPG water will regenerate approximately every 5-7 days.

NSF Certification

Testing and certification by NSF International (formerly National Sanitation Foundation) that verifies a water treatment product performs as claimed. Key standards include NSF 44 (softeners), NSF 53 (health contaminants like lead), and NSF P473 (PFAS).

Chloramine

A disinfectant made by combining chlorine with ammonia, used by many larger water systems as an alternative to free chlorine. Chloramine is more stable and lasts longer in distribution pipes but requires catalytic carbon (not standard carbon) for removal.

Action Level

A concentration of a contaminant that triggers regulatory action by the water utility, though it is not technically a violation. The lead action level is currently 15 ppb, dropping to 10 ppb in November 2027 under the LCRI. Measured at the 90th percentile of household samples.

Water Hardness

A measure of dissolved calcium and magnesium in water, typically expressed in PPM or GPG. Hard water is not a health hazard but causes scale buildup in plumbing, reduces soap effectiveness, and shortens appliance life. The USGS classifies water above 120 PPM as hard.

Salt-Free Conditioner

A water treatment device that uses Template Assisted Crystallization (TAC) or other technology to change the form of hardness minerals so they do not stick to surfaces, without removing them from the water. Does not produce soft-feeling water but can prevent scale.

Softened Water

Water that has had calcium and magnesium ions removed through ion exchange, typically replaced with sodium ions. Softened water lathers more easily, leaves no scale, and feels slippery on skin.

DBPs (Disinfection Byproducts)

Chemical compounds formed when disinfectants like chlorine react with naturally occurring organic matter in water. THMs (trihalomethanes) and HAAs (haloacetic acids) are the most common. Long-term exposure at high levels is linked to increased cancer risk.

Methemoglobinemia (Blue Baby Syndrome)

A potentially fatal condition in infants under 6 months caused by nitrate in drinking water above 10 mg/L. Nitrate interferes with the blood's ability to carry oxygen. Formula-fed infants are at highest risk.