Water Quality Explained
What the term water quality really covers, how water reaches your tap and how to make sense of the numbers in a water quality report.
What water quality actually means
Water quality is not a single property. It is a collection of measurements, each describing a different characteristic of the water. Scientists generally group these measurements into four categories.
Physical measurements describe what you can see and feel, including color, cloudiness (turbidity), temperature, and odor. Chemical measurements cover dissolved substances such as minerals, metals, nitrate, chlorine, and human-made compounds like PFAS. For example, Certified PFAS water testing in Manhattan focuses on a particular group of chemical contaminants. Microbiological measurements look for bacteria, viruses, and parasites. Radiological measurements examine naturally occurring radioactive elements, such as radon or uranium, which may be present in some groundwater.
A glass of water can meet expectations in one category while showing a problem in another. That is why the phrase “water test” tells you very little on its own until you know which measurements were included.
Where your water comes from
Drinking water starts either as surface water (rivers, lakes and reservoirs) or groundwater (aquifers reached by wells). Surface water is more exposed to runoff and microorganisms, while groundwater tends to pick up dissolved minerals, iron, manganese and sometimes arsenic or radon from the rock around it.
New York City’s water, for example, comes mainly from upstate reservoirs in the Catskill and Delaware watersheds, with a smaller supply from the Croton system. Many towns in New Jersey and Connecticut draw on a mix of reservoirs and wells, and millions of homes in the region rely on private wells.
What happens at the plant, and what happens after
Public water systems disinfect water, adjust its chemistry, and filter it in many locations. They also use corrosion control to reduce the likelihood of metals dissolving from pipes into the water.
After treatment, water may travel many miles through distribution mains, pass through a service line into a building, and then move through the building’s own plumbing. At each stage, its quality can change. Water may pick up metals, lose disinfectant while sitting unused, or collect sediment that settles inside pipes and tanks. Environmental water testing services in NYC can help investigate water quality concerns that may arise along this journey.
That is why water leaving a treatment plant and water flowing from your kitchen faucet are not always the same.
Terms you will see in a water quality report
Every community water system publishes an annual water quality report, often called a Consumer Confidence Report. These are the terms that appear most often.
| Term | What it means |
|---|---|
| MCL (Maximum Contaminant Level) | The highest level of a contaminant legally allowed in drinking water. It is an enforceable limit. |
| MCLG (Maximum Contaminant Level Goal) | The level below which there is no known or expected health risk. It is a goal, not a legal limit, and for some contaminants such as lead it is zero. |
| Action level | A level that, if exceeded in enough samples, requires the water system to take further steps. Lead and copper are managed this way. |
| ppm / ppb / ppt | Parts per million, billion or trillion. One part per billion is roughly one drop in a large swimming pool. |
| Non-detect (ND) | The laboratory did not find the substance above its reporting limit. It does not always mean zero. |
When it makes sense to test your own water
Your utility's report describes the water system as a whole, not your particular tap. Testing your own water is worth considering when:
- You use a private well. Well water is not regulated like public water, so testing is the owner's responsibility.
- Your building is older. Homes and apartment buildings built before the late 1980s may contain lead pipes, lead solder or older brass fittings.
- Something has changed. A new color, odor or taste, recent plumbing work or a nearby main break can all change your water.
- Someone vulnerable lives with you. Infants, young children and pregnant people are more sensitive to contaminants such as lead and nitrate.
- You are buying or selling a property. A test gives both sides a documented starting point.
Questions about your own tap?
Olympian Water Testing collects samples on site and uses NELAP accredited laboratories, with testing tailored to your property and your concern.