Water quality · Glossary

Water report words, in plain English

Your water quality report, a softener salesperson and this site all use the same alphabet soup. Here’s what each piece means for an ordinary home.

Short answer

PFAS (“forever chemicals”) are long-lasting manufactured chemicals; PFOA and PFOS are the two the U.S. Environmental Protection Agency (EPA) limits to 4 parts per trillion (ppt), about one drop in 20 Olympic pools. Hardness is calcium and magnesium, measured in grains per gallon (gpg); it causes scale, not illness. An MCL is a legal limit, while a health reference level is only a screening number.

A printed multi-page water quality report spread on a wooden table next to a cup of coffee and a pen. — Your utility mails or posts this report every year. It’s also called a Consumer Confidence Report.

01 · In the water

PFASper- and polyfluoroalkyl substances, "forever chemicals": A family of thousands of manufactured chemicals used in many consumer and industrial products. They break down very slowly, so they build up in water, soil and people. EPA regulates six of them in drinking water.; EPA’s PFAS rule, explained →
PFOA and PFOS: The two PFAS that EPA regulates most tightly. The legal limit for each is 4 parts per trillion. When a report says "PFAS," these two are usually the ones that matter.; The limits and the deadline →
Hardness: Calcium and magnesium dissolved in water. It causes scale and spots, not illness; EPA has no limit for it. Measured in grains per gallon (gpg) or milligrams per liter (mg/L).; Hard water, explained →
Chlorine: The disinfectant most utilities add so germs can’t grow in the pipes. It’s what gives some tap water a faint pool smell, and ordinary carbon filters remove it.; Chlorine vs. chloramine →
Chloramine: Chlorine combined with a little ammonia. It lasts longer in long pipe networks, so many big cities use it. It’s harder to filter than chlorine and must be removed for fish tanks and dialysis.; Chlorine vs. chloramine →
Lithium: A metal found naturally in some rock and groundwater. There’s no legal limit in drinking water; EPA screens results against 10 micrograms per liter (µg/L) while it studies it.; Lithium in tap water: the research →
TDStotal dissolved solids: Everything dissolved in the water added together: minerals, salts and metals. A high number affects taste and can leave residue. It says nothing about which substances are in there.
Lead service line: The pipe that runs from the water main under the street to a house, when it’s made of lead. Older homes may still have one. Utilities had to publish an inventory of theirs in October 2024.

02 · Units

pptparts per trillion, also written ng/L: A tiny amount: about one drop in 20 Olympic swimming pools. PFAS are measured in ppt because their limits are so low.; What 4 ppt means for PFAS →
ppb and µg/Lparts per billion, micrograms per liter: A thousand times more than a ppt. Lithium and lead are usually reported in ppb. 1 ppb is the same as 1 µg/L.; Lithium, measured in µg/L →
mg/L and ppmmilligrams per liter, parts per million: A thousand times more than a ppb. Hardness, chlorine and TDS are reported this way. The two units are the same number in water.; Hardness in mg/L and gpg →
gpggrains per gallon: The unit softener makers and test strips use for hardness. 1 gpg is 17.1 mg/L. Over about 7 gpg, most homes notice scale.; Softener sizing calculator →

03 · Rules and records

MCLmaximum contaminant level: The legal limit for a substance in tap water, set by EPA. Utilities must stay under it, often judged on averages over time rather than a single sample.; The PFAS limits, as an example →
MCLGmaximum contaminant level goal: The level with no known health risk, set as a goal rather than a law. For PFOA and PFOS the goal is zero, so EPA set the legal limit at the lowest level labs can reliably measure.; Why PFOA and PFOS have a goal of zero →
Health reference levelHRL: A screening number EPA uses for substances it doesn’t regulate yet, like lithium. Going over it isn’t a violation; it flags where EPA is looking.; How the lithium level was set →
UCMR 5Fifth Unregulated Contaminant Monitoring Rule: EPA’s national testing program for substances it may regulate. From 2023 to 2025 it sampled every water system serving more than 3,300 people for 29 PFAS and lithium. Most PFAS numbers you’ll see come from it.; What it found in 40 large systems →
Water quality reportConsumer Confidence Report, CCR: The yearly report every community water system has to give its customers, listing what it found in the water. It’s where our hardness numbers come from.
Health-based violation: When a utility goes over a legal limit or skips a required treatment step. Missing a paperwork deadline is a different, non-health violation.
Water system IDPWSID: The ID EPA gives every public water system, like AZ0407025 for Phoenix. It’s how EPA’s records, and ours, keep systems straight.; Find your water system by ZIP code →
SDWISSafe Drinking Water Information System: EPA’s federal database of water systems, who they serve, and their violations.

04 · Treatment

Water softenerion exchange: A tank of resin beads that trades calcium and magnesium for sodium or potassium. It’s the usual way to remove hardness for a whole house; reverse osmosis also removes it, usually just for drinking water. It recharges itself with salt water, called regenerating.; What size softener you need →
Grain capacity: How much hardness a softener can remove before it has to regenerate, like 32,000 grains. Bigger households and harder water need more.; Sizing calculator →
Salt-free conditioner: A system that changes hardness minerals so they form less scale, without removing them. Your water still tests hard afterward. It isn’t a softener, even when it’s sold as one.; Salt-free vs. salt-based →
Reverse osmosisRO: A filter that pushes water through a membrane fine enough to block most dissolved substances, including PFAS and minerals. Usually installed under one sink for drinking water.; Under-sink filters and reverse osmosis →
Catalytic carbon: A specially treated carbon that removes chloramine much better than ordinary carbon. Look for it if your city uses chloramine.; Filtering chloramine →
NSF/ANSI certification: Independent proof that a filter does what it claims. Each number is a different test: 42 for taste and chlorine, 44 for softeners, 53 for health-related contaminants like lead and PFOA/PFOS, 58 for reverse osmosis. Check that the certification names the substance you care about.; Certified drinking water filters →
Whole-house vs. point-of-use: A whole-house system treats every tap where water enters the home. A point-of-use filter treats water where it’s used, usually a drinking faucet at the kitchen sink, sometimes also the refrigerator line. Softeners are whole-house; PFAS filters are usually point-of-use.; Whole-house filters and what they cost →