What Is Water Quality and Why Is It Important?

The characteristics that define water, such as its clarity, acidity, presence of biological material, and minerals, which can vary widely from one body of water to the next. How the quality of the water is assessed generally depends on how it is going to be used. For example, is the water going to be used for drinking, bathing, or washing? Will it be used as a coolant in industrial processes? Will it be used for agriculture or for recharging an aquifer? Ultimately, the characteristics that define water quality determine whether its use is appropriate for a particular purpose.


Continue reading to learn more about the many factors that play a role in measuring water quality.

What Is Water Quality?

 According to the USGS, “Water quality can be thought of as a measure of the suitability of water for a particular use based on selected physical, chemical, and biological characteristics.” Essentially, when someone asks the question, “What is water quality?” or “What makes good water quality?” they’re usually referring to several specific measurement characteristics, such as:

  • Clarity
  • Taste
  • Odor
  • Safety
  • Chemical and mineral composition (beyond hydrogen and oxygen)  

Water quality assessments vary not only by their characteristics, but by the consumer usage. For example, municipal water departments, individual consumers, and industrial users each have different standards for water quality.


Municipalities are ultimately responsible for the quality of water distributed under their watch to both businesses and individuals. Whether they operate their own water utility, buy water from another municipality, or contract a private utility to produce and distribute water, municipal governments must ensure that the quality of water distributed within its boundaries meet all state and federal requirements.

Learn more about the municipal water treatment process that enables suitable water quality in the US.


As you can imagine, businesses use water in many ways and it can be the case that even within a particular business sector, water use varies greatly. For example, irrigation water is used to sustain plant growth, but also for chemical application, crop cooling, weed control, dust suppression, and leaching salts from root zones. Each use requires different water qualities.


Every July 1, drinking water suppliers are required under the federal Safe Drinking Water Act to issue a Consumer Confidence Report (CCR) to residents. The CCR reports on the quality of the drinking water in the area, based on the presence of lead, copper, chlorine residual levels, disinfectant byproducts, pH levels, and corrosion control chemicals (such as orthophosphate).
How Are Water Quality Standards Developed?
Water quality standards are provisions of state, territorial, authorized tribal or federal law that describe the desired condition of a water body, how that water can be used, and what actions must be taken for the water to achieve or maintain these standards. For example, local and state governments must describe what actions are in place to stop certain pollutants from entering the water. In determining how water quality is measured state and local governments must also set numerical limits, for example, parts per billion for pollutants, or state that water must be free of certain pollutants.

The U.S. Environmental Protection Agency must review and approve or disapprove each submission from a state, territorial, or authorized tribe as being consistent with the federal Clean Water Act.

If the U.S. EPA approves the standards set by the state or local government, the standards are set and must be reviewed at least every three years. If the U.S. EPA decides that the water quality standards do not meet the requirements of the Clean Water Act, the federal agency specifies the remediation required. The Water Quality Standards Program operates under Section 303 of the Federal Water Pollution Control Act (Clean Water Act), 1972 (33 U.S.C. 1313(c)).
What Are Water Quality Parameters?

In approving state and local rules governing general water quality, the U.S. EPA considers three aspects: designated use, criteria used to describe the designated uses, and antidegradation requirements.

Designated uses include, for example:

  1. Protection and propagation of fish, shellfish and wildlife
  2. Recreation
  3. Public drinking water supply
  4. Agricultural, industrial, navigational and other purposes.

Criteria can be numeric (e.g., the maximum pollutant concentration levels) or narrative. Typically, both numeric and narrative criteria are adopted.

Antidegradation requirements are those rules that aim to protect water from a loss of water quality.

What Are The Four Main Indicators Of Water Quality?

There are many parameters in assessing the quality of water. As noted above, the parameters are generally determined by the water’s intended use. For example, drinking water standards will be different than those governing the use of non-potable water used in watering a public golf course.


Water turbidity is the measure of its relative clarity. That is, the degree to which it is cloudy, clear or opaque. Turbidity is caused by light reflecting off material suspended in the water. That material could be clay, silt, inorganic and organic matter, algae, dissolved colored organic compounds, and microscopic organisms.
Turbidity is measured in nephelometric turbidity units (NTU). High turbidity levels—that is, higher than 10 NTU, often caused by heavy rain disturbing soil in riverbanks, can be harmful to fish and other aquatic life. Particles found in turbid water also provide places for other pollutants, such as metals and bacteria.
Turbid water is aesthetically unappealing but does not necessarily pose health risks to a human. Still, because turbidity can provide shelter for pathogens, it’s better to reduce it whenever possible.


pH is a measure of relative amount of free hydrogen and hydroxyl ions in the water. Simply put, it’s how acidic or basic (alkaline) water is. Measured on a scale of 0 to 14, water that is less than 7 is considered more acidic. Water that has more free hydrogen ions is acidic, whereas water that has more free hydroxyl ions is basic.

Why does pH matter? Well, for one reason, the pH of water reflects the solubility of chemical constituents such as nutrients (e.g., nitrogen, phosphorus, and carbon) and heavy metals (e.g., copper, lead and cadmium). The greater their solubility—that is, their ability to dissolve in water—the more toxic they are. Metals tend to be more toxic at lower pH because they are more soluble.


Phosphorus is an essential element for plant life, but an excess of phosphorous in water reduces dissolved oxygen, leading to algae blooms and death of aquatic animals. Phosphorus is a common constituent of agricultural fertilizers, manure, and organic wastes in sewage.


Nitrogen, in the forms of nitrate, nitrite or ammonium, is a nutrient needed for plant growth. About 78 percent of the air that we breathe is composed of nitrogen gas, and in some areas of the United States, particularly the northeast, certain forms of nitrogen are commonly deposited in acid rain. Like phosphate, high levels of nitrogen in water are harmful to the aquatic ecosystem.
Why Is It Important To Test Water Quality?

Our lives and health depend on high-quality water. That’s why it’s important to test water quality regularly. Some pollutants, for example, E. coli O157:H7, can affect human health quickly (water containing this strain of E. coli typically causes health symptoms in four to seven days). Other pollutants, such as lead, can take years to show their detrimental effects.

So, how do you test for water quality? SUEZ regularly conducts water supply quality testing before, during and after the treatment process to ensure it meets or surpasses regulatory standards, monitoring for lead, copper, corrosion and pollutants. SUEZ technologies help to maintain water quality control from treatment to tap. Each year, we issue an Annual Consumer Confidence Report (CCR) for every water source we touch, demonstrating how our drinking water measures up to regulatory standards.

Why Should Water Quality Matter To You?

Water quality affects every aspect of our lives. It’s no secret that our very health and well-being depend on the availability of clean water. The misuse and overuse of water, as well as climate change, have required greater efforts to clean and maintain our water supplies.

Many factors can affect the quality of your water. For homeowners, this includes the plumbing in your home, the proximity of sewers and wastewater collection systems, your municipal water suppliers and the monitoring and enforcement of industrial effluent.

For businesses, clean water is essential if you are to maintain high-quality goods and services, avoid fines and penalties, and maintain the health and good will of your clients. And for municipalities, you are obligated—both morally and legally—to provide safe water to your residents and businesses.

Contact a representative to learn more about our water quality monitoring and management offerings for your business or municipality.