How to Read Your Water Quality Report

Posted by
John Woodard on May 12, 2023

Each year, a water supplier must provide a Consumer Confidence Report (CCR) that details the quality of its water. Because tap water is used every day, it is important for customers to understand the contents of their local water quality report. With proper knowledge, a consumer of city-treated water can set up systems in their home to produce the highest quality water for themselves and their families. Below you can find information about the importance of water quality reports, common report terms, the contaminants listed in these reports, and the effects of contaminants that are left out of reports.

Why is a water quality report important?

A water quality report contains vital information about the contamination levels in your municipality’s treated water. Water quality reports only include primary contaminants, those that can negatively impact health at levels typically found in water. While all city-treated water must meet safety standards set by the EPA, the standards at which city water treatment is held are considered safe to a reasonable level. However, the cost to achieve water quality that is undoubtedly safe for drinking is unrealistic for treatment plants in terms of cost and efficiency. Water filtration systems in the home can effectively bridge the gap between tap water quality and water that is undeniably healthy long-term. Understanding a water quality report allows a homeowner to know which contaminants are highest in their tap water and install a proper home water treatment system accordingly.

Learn more: What is a whole house water filtration system?

Common water quality report terms

how to read a water quality report example

Common terms found in water quality reports include:

  • Parts per million (ppm) – 1 ppm indicates that there is one part of contaminant for every one million parts of water present.
  • Parts per billion (ppb) – 1 ppb indicates that there is one part of contaminant for every one billion parts of water present.
  • MCL – maximum contaminant level. This number, expressed in ppm or ppb, indicates the maximum concentration of a primary contaminant allowed in a public water supply. For example, the MCL set by the EPA for iron in drinking water is 0.3 ppm (300 ppb). The MCL, unlike the MCLG, is enforceable by the EPA. These standards were established under the Safe Drinking Water Act.
  • MCLG – maximum contaminant level goal. The MCLG, like the MCL, sets a standard for contaminant concentration in drinking water. Unlike MCL, the MCLG of a contaminant is not enforceable. Rather, it is the contamination level where no adverse health effects are associated at or below that level. When the MCL differs from the MCLG, there is typically an issue with treatment cost that hinders treatment plants from being able to reach the smaller contamination level. For example, the MCL of lead in drinking water is 15 ppb, but the MCLG is zero. This means that any amount of lead contamination in water is hazardous to health. However, the cost of completely removing lead from water supplies is not attainable in a practical sense, so very small amounts of lead are allowed in tap water.
  • MRDL – maximum residual disinfectant level. This refers to the maximum amount of disinfectant allowed during the water treatment process. Like the MCL, the MRDL is enforced by the EPA.
  • MRDLG – maximum residual disinfectant level goal. Levels of disinfectant at or below this value are not known to negatively affect health. This is similar to MCLG, but it refers to the safe levels of disinfectant used in water treatment rather than the contaminants present.
  • TT – a treatment process that must be performed to reduce the contaminant’s presence in water.
  • Range – lowest and highest levels at which the contaminant was found in the water.
  • Violation – indicates if the MCL has been exceeded. This column will either be labeled with a “yes” or a “no” for each contaminant.
  • Source – the place, process, or items that the contaminant originates from. Examples of contamination sources include erosion, runoff, industrial waste, and intentional addition during treatment.


Contaminants in water quality reports

The EPA currently sets regulations on over 90 contaminants in drinking water. Each contaminant is placed into one of four categories:

  • Physical. Physical contaminants alter the physical characteristics of water, such as color and texture. Soil, sediment, algae, and other organic material are examples of physical contaminants.
  • Chemical. Chemical contaminants are natural or synthetic chemicals that make their way into water. Examples of chemical contaminants include pesticides, salts, bleach, and nitrogen.
  • Biological. Biological contaminants refer to microbial and microbiological contaminants. These include bacteria, viruses, and parasites.
  • Radiological. Radiological contaminants are capable of emitting ionizing radiation. These contaminants include uranium, plutonium, and cesium.

All four types of contaminants can be hazardous to health, but some within each category are more dangerous than others. Below are the most common or hazardous contaminants listed in water quality reports.


lead pipes

Lead is one of the most toxic contaminants in drinking water. Unlike many contaminants, the MCLG of lead in drinking water is zero. This means that any intake of lead is known to negatively impact health in either the short or long term. Lead is a particular problem in older homes with lead pipes. To combat lead contamination in water, the Lead and Copper Rule was established in 1991. This rule set an upper bound for both copper and lead levels. If this limit is reached by the 90th percentile of tap water samples, further action must be taken to limit corrosion, monitor water quality parameters, and replace lead service lines. The current MCL of lead in drinking water is 15 ppb. As water treatment technology improves over time, this level may be decreased to a level closer to the MCLG.

Learn more: How to remove lead from water


Fluoride is added to water supplies to improve oral health. In the “Source” column for fluoride, your local water supplier should indicate the addition of fluoride to the water supply. The MCL of fluoride in drinking water is 4 ppm, but the recommended level of fluoride is 0.7 ppm. As a result, most water suppliers add enough fluoride for the contamination level to sit at around 0.7 ppm. Some controversy has surrounded the addition of fluoride to water supplies. Consequently, some homeowners opt to filter out fluoride in their water before consuming it.

Learn more: How to remove fluoride from water


Arsenic is a contaminant that most commonly reaches water supplies through pesticides and herbicides. Like lead, arsenic is an extremely toxic element. Because of its toxicity, arsenic’s MCLG is set to zero by the EPA, and its MCL currently sits at 10 ppb. Because there is an allowed level of arsenic in tap water, many homeowners incorporate a filtration system that can remove arsenic from their home’s water. If you want a hands-on approach to checking the levels of arsenic in your home, you can test your water with an arsenic test kit.

Learn more: How to remove arsenic from water


microorganisms in water

Many microorganisms are regulated by the EPA, including cryptosporidium, giardia lamblia, legionella, and coliform bacteria. The MCLG of each of these microorganisms is zero. To kill bacteria in water, chlorine is added, but this does not kill some resistant microorganisms, such as cryptosporidium. To effectively treat chlorine-resistant microorganisms, coagulation, flocculation, sedimentation, and other filtration processes must be used. These treatment steps, alongside the addition of chlorine, allow consumers to be safe from the hazardous effects of microorganisms.

Learn more: How to remove bacteria from water | How does city water treatment work?


Nitrate is a contaminant that reaches water through soil runoff, septic systems, wastewater, landfills, and other sources. The MCL of nitrate in drinking water is 10 ppm. Concentrations of higher than 10 ppm can cause harsh symptoms, such as muscle weakness, fast heart rate, dizziness, and fatigue. Pregnant women and women attempting to become pregnant are most at risk of symptoms of nitrate consumption. The MCLG of nitrate is also set to 10 ppm, so the tap water standards for nitrate should not cause negative health effects over any length of time.

Learn more: How to remove nitrates from water


Nitrite reaches groundwater through the same sources as nitrate, but it is slightly more toxic. Because of this, the MCL of nitrite, set at 1 ppm, is lower than that of nitrate. Consuming over 1 ppm of nitrite can lead to side effects like headaches, nausea, shortness of breath, confusion, and dizziness. Like nitrate, the MCLG of nitrite is identical to its MCL of 1 ppm, meaning its concentrations in tap water should not cause any adverse effects on human health.

What contaminants are not listed in a water quality report?

Secondary contaminants are those which do not pose health risks, but they do change the appearance, smell, taste, or other properties of water. Because these elements do not pose health risks, each secondary contaminant’s MCL, known as secondary maximum contamination level (SMCL) is not enforced. Rather, SMCLs are a suggested contamination level that should not be exceeded when possible. The most common secondary contaminants in drinking water are calcium, magnesium, and aluminum.

Calcium and magnesium

The most notable of contaminants not included in a water quality report are the water-hardening minerals calcium and magnesium. These elements do not cause negative health effects, so they are not regulated by the EPA. However, they can cause some undesirable effects inside the home. When calcium and magnesium contaminate water that runs through plumbing, pipes become coated in limescale that builds up over time. Limescale is also hazardous to appliances. Dishwashers, washing machines, and water heaters all live shorter lives when subjected to limescale regularly.

Learn more: How to prevent limescale buildup in your home

limescale on faucet

The most effective ways to reduce limescale buildup in a home are a water softener or water conditioner. Water softeners completely reduce the presence of water-hardening minerals in water, while water conditioners crystallize these minerals. Water conditioners utilize salt to neutralize calcium and magnesium, while water conditioners do not. As a result, water conditioners are better for the environment because they do not pollute wastewater with salt.

Learn more: Water Conditioners vs Water Softeners | The truth about salt-free water softeners | What is a water softener?


Aluminum is a common secondary contaminant that everyone consumes on a regular basis. The SMCL of aluminum in drinking water is between 0.5-2 ppm. This level prevents aluminum from changing the color of water. When exposed to high levels of aluminum, the body will suffer side effects, such as muscle weakness, bone pain, and confusion. However, the levels at which aluminum is present in water do not pose a threat to human health.




If you have any additional questions, please do not hesitate to contact us.

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