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Glossary

Water Quality Glossary

Definitions for the terms used throughout this site, grouped by topic. Most come directly from your Consumer Confidence Report, New York's the school lead-in-water testing regulation school testing framework, or common well and treatment-equipment terminology.

Reports & regulations

• CCR (Consumer Confidence Report): The annual water quality report every community water system must provide to customers.
• MCL (Maximum Contaminant Level): The legal, enforceable limit for a substance in drinking water.
• MCLG (Maximum Contaminant Level Goal): The level below which there is no known or expected health risk; sometimes lower than the MCL.
• SMCL (Secondary Maximum Contaminant Level): A non-enforceable guideline for substances that mainly affect taste, odor, color, or staining rather than health — iron and manganese are common examples.
• MRDL (Maximum Residual Disinfectant Level): The highest allowed level of a disinfectant (such as chlorine or chloramine) remaining in water after treatment.
• AL (Action Level): Used for lead and copper — the concentration that triggers required action if exceeded.
• TT (Treatment Technique): A required process rather than a numeric limit.
• ppb / ppm: Parts per billion / parts per million — the units most water test results are reported in.
• ND: Not detected — tested for, not found above the lab's detection threshold.
• SDWA (Safe Drinking Water Act): The 1974 federal law that gives EPA authority to set enforceable drinking water standards for public water systems nationwide.
• NPDWR (National Primary Drinking Water Regulations): The specific enforceable rules EPA issues under the SDWA, each setting an MCL or treatment technique for a given contaminant or group of contaminants.
• Lead and Copper Rule (LCR): The federal regulation governing how public water systems monitor for lead and copper and respond when the action level is exceeded.
• UCMR (Unregulated Contaminant Monitoring Rule): An EPA program requiring periodic monitoring of contaminants that aren't yet regulated, used to decide whether future regulation is needed.
• WIIN Act: The federal Water Infrastructure Improvements for the Nation Act, which funds programs including NY's voluntary school and child care lead testing program.
• School lead-in-water testing regulation (10 NYCRR Subpart 67-4): The New York law requiring every public school district and BOCES to periodically test drinking-water outlets for lead and remediate any outlet at or above the 5 ppb action level.
• 3Ts: EPA's Training, Testing, and Taking Action framework for reducing lead in school and child care drinking water.
• Standard of identity: FDA's rules defining what can legally be labeled "spring water," "purified water," and other bottled water categories.
• Standard of quality: FDA's contaminant limits for bottled water, required to be no less protective than EPA's tap water standards.
• CGMP (Current Good Manufacturing Practice): FDA rules requiring bottled water to be produced and bottled under sanitary conditions.

Government agencies

• EPA: The U.S. Environmental Protection Agency, which regulates public tap water nationwide under the Safe Drinking Water Act.
• FDA: The U.S. Food and Drug Administration, which regulates bottled water as a packaged food product.
• CDC: The Centers for Disease Control and Prevention, which publishes national guidance on private well testing and public health topics like fluoride in infant formula.
• NYSDOH: The New York State Department of Health, which enforces drinking water standards and accredits testing labs within the state.
• NY DOH: The New York Department of Health, which publishes private well testing guidance and tracks well-water studies statewide.
• NYSED: The New York State Education Department, which works with NYSDOH on school drinking-water requirements.
• NY PUC: The New York Public Utility Commission, which regulates investor-owned and some municipal water utilities operating in the state.
• WQA (Water Quality Association): The water treatment industry's trade association, which administers the Gold Seal product certification program and Certified Water Specialist / Certified Installer professional certifications.

Water systems

• PWS (Public Water System): Any system providing piped water for human consumption to at least 15 connections or 25 people for 60+ days a year — the broad legal category covering municipal utilities and similar providers.
• CWS (Community Water System): A public water system serving the same year-round residents — the category most homes are on, and the one required to issue a CCR.
• NTNCWS (Non-Transient Non-Community Water System): A public water system that regularly serves the same people for 6+ months a year but not year-round residents — a common classification for schools and workplaces with their own water source.
• Source water: The river, reservoir, or aquifer a public water system draws from before treatment — identified in every CCR.
• Gold Seal: WQA's independent, third-party certification confirming a water treatment product actually performs to its advertised claims — the oldest such certification program in the industry.

Home treatment & filtration

• Activated carbon (GAC): A porous, carbon-based filter media — made by heat-treating material like coconut shell or coal — that adsorbs chlorine, many organic compounds, and taste- or odor-causing substances as water passes through.
• Ion exchange: The process behind water softening — water passes over a resin that trades its own sodium (or potassium) ions for the calcium and magnesium ions causing hardness.
• Resin: The manufactured beads inside a softener's tank that carry out ion exchange; they gradually lose capacity and are recharged during regeneration.
• Brine: The concentrated salt solution a softener flushes through its resin during regeneration to rinse off collected hardness minerals and recharge the resin.
• Regeneration: The cycle a softener runs periodically to flush brine through its resin bed, removing built-up hardness minerals and restoring softening capacity.
• Salt bridging: A hardened crust of salt that forms in a brine tank and stops loose salt from dissolving into the water below — prevents proper regeneration until cleared.
• Iron fouling: A buildup of iron on or inside a resin bed or filter media that reduces its capacity over time — a common reason well-water softeners need more frequent attention.
• Template-assisted crystallization (TAC): The mechanism behind salt-free water conditioners — it alters the crystal structure of hardness minerals so they're less likely to form visible scale, without removing them from the water.
• Reverse osmosis (RO): A filtration method that pushes water through a semipermeable membrane under pressure, separating purified water from a concentrated reject stream — the reverse of how water naturally moves toward a more concentrated solution.
• Semipermeable membrane: A thin, engineered filter material with pores small enough to pass water molecules while blocking most dissolved salts, particles, and larger molecules — the core component of an RO system.
• Nanofiltration: A membrane process between reverse osmosis and ultrafiltration, used less often in residential systems, that removes somewhat larger particles at lower pressure than RO.
• Ultrafiltration: A membrane process that removes small colloids and large molecules but passes more dissolved minerals through than reverse osmosis does.
• Microfiltration: The most open of the common membrane processes, removing larger particles and some microorganisms but not dissolved contaminants.
• Activated alumina: A treatment media that adsorbs specific contaminants, including fluoride and arsenic, and requires periodic regeneration to keep working.
• Ozonation: A disinfection and oxidation method that feeds ozone gas into water, used in some treatment systems as an alternative or supplement to chlorine.
• Sequestering agent: A chemical that binds to dissolved metal ions (like iron or manganese) so they stay dissolved instead of precipitating out and causing staining.
• Orthophosphate: A corrosion-control compound some utilities add to water to form a protective film inside pipes, reducing lead and copper leaching from older plumbing.
• Point of entry (POE): Treatment installed where the main line enters a building, conditioning all water before it branches to individual fixtures — how whole-house filters and softeners are installed.
• Point of use (POU): Treatment installed at a single fixture, such as an under-sink RO system at the kitchen tap, rather than for the whole building.
• Micron rating: A measurement of the smallest particle size a filter is built to capture; a lower micron rating traps finer particles but typically needs more frequent replacement.
• NSF/ANSI standard: Independent testing standards (such as NSF/ANSI 42, 53, and 58) that verify a specific product actually reduces the contaminants it claims to — worth checking before buying any filter, softener, or RO system.
• Purified water: An FDA labeling category for water that meets a defined purity specification, achievable by reverse osmosis, distillation, deionization, or another suitable method — RO is one way to get there, not the only one.
• UV disinfection: A treatment stage that uses ultraviolet light to inactivate bacteria and other microorganisms without adding any chemical residual; mainly relevant for wells with a confirmed microbial concern.
• Catalytic carbon: A specialized carbon media that reduces chloramine effectively, unlike standard activated carbon, which is built primarily for chlorine.
• KDF media: A copper-zinc alloy filter media, often used as a pre-filter alongside carbon, that helps control bacterial growth within the filter and reduce certain dissolved metals.
• Bypass valve: A valve installed alongside whole-house treatment equipment that lets water skip the system temporarily, so the household isn't without water during filter changes or servicing.
• Reject stream (concentrate): The portion of incoming water an RO membrane routes away as it separates out dissolved solids, carrying the rejected material to the drain.
• Permeate: The purified water that has passed through an RO membrane — the product water on the clean side of the process.
• Remineralization: An optional RO system stage that adds back trace minerals for taste after the membrane process removes them along with contaminants.

Water quality & contaminants

• Hardness: Dissolved calcium and magnesium in water, measured in grains per gallon (gpg — one grain equals about 17.1 ppm). Rough guide: under 1 gpg is soft, 1–3.5 gpg slightly hard, 3.5–7 gpg moderately hard, 7–10.5 gpg hard, and above 10.5 gpg very hard.
• PFAS: A group of manufactured chemicals ("forever chemicals") that are an emerging area of drinking water regulation.
• Fluoride: A naturally occurring mineral in some water supplies, regulated because levels well above normal ranges have been linked to dental and, at much higher concentrations, skeletal effects.
• Coliform bacteria: A group of bacteria naturally present in soil, vegetation, and the intestines of humans and animals, tested for as a general indicator of whether a water system may be vulnerable to contamination.
• Nitrate / nitrite: Compounds most often linked to agricultural runoff and septic systems, part of the core annual test panel recommended for private wells alongside coliform bacteria, TDS, and pH.
• Arsenic: A naturally occurring element sometimes found in groundwater at levels of concern; one of the metals NY DOH-reviewed USGS well studies have flagged in a small share of tested wells.
• Barium: A naturally occurring metal occasionally found in well water above regulatory limits, alongside arsenic one of the more commonly flagged metals in NY groundwater studies.
• Total dissolved solids (TDS): A measurement of all dissolved minerals and salts in water, in parts per million; often checked with a simple meter to gauge how well an RO membrane is performing.
• Total organic carbon (TOC): A measurement of carbon-containing compounds in water, used partly to gauge how much disinfection byproduct formation might occur when chlorine is added.
• Turbidity: A measure of cloudiness caused by suspended particles, measured in NTUs; high turbidity can shield microorganisms from disinfection.
• Alkalinity: A water sample's capacity to neutralize acid, reported as calcium carbonate equivalent — related to, but not the same measurement as, pH.
• Conductivity: A measure of how well water conducts electricity, which rises with dissolved mineral and salt content; often used as a quick proxy for TDS.
• Chlorine / chloramine: The two disinfectants most public water systems use to control bacteria in the distribution system. Chloramine (a chlorine-ammonia compound) persists longer in the system but needs catalytic rather than standard carbon to filter effectively.
• Iron (ferric iron): Dissolved or suspended iron in water, often visible as rusty discoloration or staining on fixtures and laundry; common in well water and typically treated with an oxidizing filter.
• Manganese: A mineral often found alongside iron in groundwater; even small concentrations can cause dark staining on fixtures and laundry.
• Hydrogen sulfide: A naturally occurring gas sometimes present in well water, responsible for the classic "rotten egg" odor; typically treated with an oxidizing filter.
• Disinfection byproducts (THMs): Compounds, including trihalomethanes, that form when chlorine reacts with naturally occurring organic material in water — regulated substances tracked in every CCR.

PFAS compounds

The specific "forever chemicals" named in EPA's 2024 national drinking water rule, referenced throughout our PFAS explainer:

• PFOA: Perfluorooctanoic acid, one of the two most studied PFAS, regulated individually at 4.0 parts per trillion (ppt).
• PFOS: Perfluorooctane sulfonic acid, regulated individually alongside PFOA at 4.0 ppt.
• PFHxS: Perfluorohexane sulfonic acid, regulated individually at 10 ppt under the 2024 rule (subject to a 2026 proposed rescission — see our PFAS explainer for current status).
• PFNA: Perfluorononanoic acid, regulated individually at 10 ppt under the 2024 rule (also subject to the proposed rescission).
• HFPO-DA (GenX): Hexafluoropropylene oxide dimer acid, regulated individually at 10 ppt under the 2024 rule (also subject to the proposed rescission).
• PFBS: Perfluorobutane sulfonic acid, regulated only as part of the Hazard Index mixture calculation, not with its own individual limit.
• Hazard Index: A combined-risk calculation (target of 1.0) EPA uses for water containing two or more of PFHxS, PFNA, HFPO-DA, and PFBS together, rather than judging each separately.

Schools & facilities

• Fixture inventory: A written list of every drinking fountain, bottle filler, and kitchen tap in a building, with location and type — the foundation of any school or facility drinking water plan.
• Corrective action: The defined response when a fixture's lead test comes back at or above the action level — typically removing it from service, investigating the cause, remediating, and re-testing before it's used again.
• Drinking water plan: A school or facility's written document covering its fixture inventory, testing decision, corrective action procedure, maintenance schedule, and point of contact.

Wells & plumbing

• Distribution system: The network of pipes and infrastructure that carries treated water from a utility's treatment plant to individual homes and buildings.
• Aquifer: An underground layer of rock, sand, or gravel that holds and carries groundwater — the source private wells draw from.
• Well casing: The pipe lining a drilled well that keeps the borehole from collapsing and helps prevent surface contaminants from entering the water supply.
• Grouting: A cement-like sealant placed around a well casing during drilling to block surface water and shallow contaminants from seeping down into the well.
• Wellhead: The above-ground access point of a well, where the casing, cap, and connections to the pump and plumbing come together.
• Static water level: The natural resting level of water in a well when the pump isn't running.
• Drawdown: How far the water level in a well drops while the pump is actively drawing water.
• Submersible pump: A pump installed inside the well casing, below the water level, that pushes water up to the home rather than pulling it from above.
• Pressure tank (hydropneumatic system): A tank using compressed air to keep water pressure available at the fixtures even when the well pump isn't actively running.
• Sacrificial anode: A metal rod inside a water heater tank designed to corrode first, protecting the tank itself from rusting through — a routine water heater maintenance item, unrelated to your water supply's quality.
• Potable water: Water that meets EPA and/or state drinking water standards and is considered safe for human consumption.
• Cross-connection: Any point in a plumbing system where a potable line could contact a non-potable source, creating a risk that contamination gets pulled backward into drinking water.
• Backflow: Water moving in the reverse of its intended direction in a pipe, usually from a pressure change — the mechanism that makes a cross-connection a contamination risk.
• Water hammer: A shock wave in household plumbing caused by water flow stopping or starting abruptly, sometimes audible as a bang in the pipes; usually addressed with an arrestor device rather than anything related to water quality.
• Lead service line: The pipe made of lead that in some older systems connects the water main to a building's plumbing — a key focus of the Lead and Copper Rule and utility replacement programs.
• Corrosion: The gradual chemical breakdown of metal plumbing or fixtures from contact with water, which over time can affect taste and, in older homes, contribute to lead or copper entering tap water.
• Scale: Mineral deposits — mainly calcium and magnesium carbonate — that build up on fixtures, inside pipes, and in water heaters when hard water goes untreated.
• First-draw sample: A sample collected straight from the tap after plumbing has sat unused for several hours (usually overnight), without running the water first — the standard method for lead testing since it captures worst-case stagnation.
• Flushing: Running water through fixtures or lines to clear out water that's been sitting still, commonly done after extended closures or as routine maintenance.

For homeowners

Questions to ask your water provider

• Can you send me the most recent Consumer Confidence Report for my address?
• Has this system had any violations in the past three years, and what was the resolution?
• Does this system use chlorine or chloramine for disinfection?
• What is the source water for my address — surface water, groundwater, or a blend?
• Is there a known hardness range for water delivered to my area?

For homeowners

Questions to ask a water treatment contractor

• Will you test my specific water before recommending equipment, or is this a standard package?
• What certification does this specific filter or system have (e.g., NSF/ANSI 42, 53, 58), and what does that certification actually cover?
• What's the full maintenance schedule and estimated annual cost of filters/salt/membranes?
• Is this system sized for my household's specific usage and hardness level, or a generic size?
• What's the warranty, and what does it not cover?
• Are you a WQA Certified Installer or Certified Water Specialist?

For schools & facilities

Questions to ask a school facility manager

• When was our building's drinking water last tested for lead under 10 NYCRR Subpart 67-4, and where are the results and any remediation documented?
• Do we have a current fixture inventory, and when was it last updated?
• What's our filter replacement schedule for bottle fillers, and is it being followed?
• Has any fixture ever tested at or above 5 ppb (New York's school action level, lowered from 15 ppb in 2023), and if so, what was done?
• Who is the designated point of contact for our drinking water plan?

Keep exploring

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FAQ

Frequently asked questions

Is this glossary specific to New York?

The terminology itself (MCL, MCLG, ppb, CCR, etc.) is federal and applies nationwide, since New York's drinking water program operates under the same federal Safe Drinking Water Act framework as other states. The county and the school lead-in-water testing regulation references on this site are NY-specific.

Can I bring a printed question list to a meeting with my provider or a contractor?

Yes — the question lists on this page are meant to be copied, printed, or read from directly when you're on a call or in person with a provider, contractor, or facility manager.

Last reviewed: July 9, 2026