An Introduction To Water Quality

An Introduction to Water Quality

What makes water “good” or “bad”? If water can be “hard” then can it also be “easy”? We’ll take a deeper look into these questions in this post about water quality, and then we’ll wrap up with a look at some organizations involved in water quality monitoring and advocacy. Let’s get started!

Water Quality Properties

Water quality involves a number of measurable physical and chemical properties, some common ones being:

  1. Temperature
  2. Acidity (or pH)
  3. Dissolved Oxygen
  4. Turbidity
  5. Specific Conductance
  6. Hardness

Let’s take a closer look at each property:


Water temperature is important for supporting all aquatic life. Temperature affects the level of oxygen, which organisms can survive and grow in certain waters, and how resistant organisms are to certain pollutants. 

One benefit of green infrastructure is that it helps regulate temperatures of nearby streams and other water bodies by soaking up harmful runoff. Not only does runoff have pollutants, such as those from motor oil or fertilizer, but runoff tends to be much higher in temperature from being in contact with pavement and asphalt, which can get quite hot on a summer day! A sudden introduction of heated runoff to a nearby pond can put stress on the resident aquatic organisms and decrease the overall water quality.

Water temperature for optimal breeding, growth, and survival for different fish species, Source: Detroit Free Press (


Water acidity, or the measurement of pH, indicates the amount of hydrogen ions (H+) present in water. Acidity is measured on a scale that ranges from 0 to 14, with 7 being neutral. A pH of less than 7 is acidic while a pH greater than 7 is alkaline, or basic. 

The change in pH in a stream or body of water can indicate that the level of certain pollutants has increased. For example, water from a coal mine is acidic and can have a pH as low as 2, so a sudden drop in a water’s pH could indicate a source of runoff has been introduced to the water. Acidity of rainfall varies throughout the country, as shown below. Rainfall tends to be slightly acidic (typically around 5.6) due to carbon dioxide in the atmosphere.

Acidity of rainfall across the U.S., Source: USGS (

Dissolved Oxygen

Like humans, fish and other aquatic organisms need oxygen to live. A small amount of oxygen, about ten molecules of oxygen per million molecules of water, is dissolved in water. ​​Cold, rapidly moving water can hold more dissolved oxygen than warm, stagnant water. 

Dissolved oxygen is typically measured in mg/L or parts per million (ppm), where levels of greater than 7 mg/L or ppm supports fish population growth and activity and levels of greater than 9 mg/L or ppm supports abundant fish populations. Certain fish species require higher concentrations of dissolved oxygen to survive. When excess organic material enters streams or water bodies, bacteria can consume a lot of the dissolved oxygen, resulting in fish die-off. When water has dissolved oxygen less than 2 mg/L, the water is classified as “hypoxic” and indicates a dead zone.

Oxygen requirements of different aquatic species.
Source: Fondriest Environmental (


Turbid water is often described as cloudy or opaque. This quality of water refers to how much particulate matter, such as clay, silt, plankton, or microscopic organisms, is suspended in water. There are different units of turbidity depending on which instrument is used, but a commonly used unit is NTU, which stands for Nephelometric Turbidity Unit.

An uptick in sedimentation can harm fish and other aquatic life. This is due to particles providing attachment places for metals, bacteria, and other pollutants. This is why turbidity readings can be a useful indicator of potential pollution.

Range of turbidity measurements in NTU, Source: Limno Loan (

Specific Conductance

Specific conductance is the capacity of water to conduct an electrical current. Conductance is related to the amount of dissolved solids, such as salt and is measured in µS/cm. Like other properties discussed so far, significant shifts in conductivity could indicate that a discharge or other pollution has entered a water body. 

Range of specific conductance for different types of water
Source: Fondriest Environmental (


Water hardness refers to the amount of dissolved calcium and magnesium present in the water. Hardness varies throughout the United States, and some regions require filters to be installed to adjust water hardness. When washing with hard water, more soap or detergent may be required to clean, as soap reacts with calcium to form soap scum. 

Hardness is measured in mg/L CaCO3, where 0-75 mg/L CaCO3 is considered soft water, and 150-300 is considered hard water. Generally, when water is harder, the toxicity of other metals will be lower to aquatic life. This is because in hard water, some of the metal ions precipitate out of the solution as insolubles, and are not available to be taken in by aquatic organisms. 

Range of water hardness, Source: Serene Aquarium (

Recent NYC Water Quality Projects

Here are some examples of organizations who are working to monitor, protect, and/or improve water quality in New York City.

1) BioBus

Scientists and students from BioBus study aquatic life in the Hudson River Estuary on the Baylander, a repurposed Vietnam-era navy warship. BioBus partnered with Temboo to deploy sensors, including one to monitor dissolved oxygen in the water. Measuring dissolved oxygen helps us determine whether the Hudson River is healthy and able to support aquatic life. Like other bodies of water in New York City, the Hudson is subject to raw sewage discharges, which lead to contaminated food webs, high bacteria counts, and low oxygen levels. 

Rob Frawley, Staff Scientist, says:

“Having our water quality monitor has allowed us to collect and share local WQ data with our research students as well as local schools in Harlem and Washington Heights. Students can use real-time DO information to assess events observed in the water and students can see long-term and seasonal trends and gain comfort in data analysis with contextualized data”

Learn more about the organization here.

2) Van Cortlandt Park Alliance (VCPA)

Previous water quality projects conducted by Van Cortlandt Park Alliance have involved studying conductivity and nitrate levels weekly as well as real-time remote monitoring of water flow depth and velocity, a collaboration with Temboo. Additionally, VCPA continues to analyze water samples for factors including total phosphorus, pH, dissolved oxygen, turbidity, and temperature. They also inventory plants and wildlife and analyze lake sediment cores.

John Butler, Program Director: Restoration & Stewardship, says:

“Van Cortlandt Park Alliance is committed to monitoring and protecting the health of Tibbetts Brook. Through this work and the advocacy of VCPA and other community groups, NYC recently purchased an evacuated railbed. This old railbed will become home to a daylighted portion of Tibbetts Brook, reconnecting the stream to the Hudson River Estuary, and running alongside the extended Putnam Greenway!”

Learn more about the organization here.

3) Guardians of Flushing Bay (GoFB)

Guardians of Flushing Bay work for healthy and equitably accessible of Flushing Waterways. The organization uses water quality sampling data as an integral advocacy tool against harmful CSO outputs.

Rebecca Pryor, Executive Director, says:

“Throughout Flushing Waterways in Northern Queens, GoFB strives to build community power around policies and projects that advance environmental and ecological justice. We use water quality data collection as one method of achieving this goal, where the collected data informs policies and projects that advance improved water health. We participate in two collection efforts: the Billion Oyster Project’s Community Water Quality Testing program, which tests for sewage indicating bacteria, and Save the Sound’s Unified Water Study, which tests for several parameters in order to get an overall snapshot of the water. Combined, we collect data across 18 different sites over 6 months.” 

Learn more about the organization here.

4) Bronx River Alliance

Bronx River Alliance staff and volunteers work together to monitor the Bronx River’s water quality, which includes taking temperature, pH, dissolved oxygen, conductivity, and turbidity measurements. They also check the water for pollutants including fecal pathogens and microplastics. Among all pollutants and factors that threaten the health of the Bronx River, the top three are floatable trash, fecal pathogens, and low dissolved oxygen.

Christian Murphy, Ecology Coordinator, says:

“The Bronx River Alliance has been working hard to restore and protect the Bronx River and its unique ecosystems for over 20 years. By periodically monitoring the water quality for parameters like dissolved oxygen, nutrients, and fecal bacteria we can identify trends in the data that point towards issues that threaten the river’s health, such as sewage overflows. We know that a healthy river depends on things like clean, healthy parks and green spaces to capture polluted stormwater and provide habitat for wildlife, and we are excited to soon be opening a new section of parkland that contains many green infrastructure features that will protect the river from pollution. We recently had two dolphins visit the Bronx River and we are celebrating the slow but steady revitalization of this beautiful natural resource!” 

Learn more about the organization and their water quality monitoring efforts here

5) Riverkeeper

Riverkeeper was founded by a group of concerned Hudson River fishermen who saw pollution threatening their livelihoods. Riverkeeper staff and volunteers work together to physically clean the river and the bordering landscape. They also conduct restoration projects, which include water quality monitoring, removing invasive species, and planting native species. 

Learn more about the organization here.

6) NYC Soil and Water Conservation District (NYC SWCD)

NYC SWCD works to protect the city’s water quality by installing green infrastructure projects and promoting stormwater infiltration practices. They are also involved in monitoring water quality factors that may indicate the presence of CSO events.

Learn more about the organization here.

7) Natural Resources Defense Council (NRDC), Northeast and Mid-Atlantic Region

Through advocacy, NRDC of the Northeast and Mid-Atlantic region fight against threats to waterways, which includes holding GE accountable in the cleanup of toxic PCBs in the Hudson River. NRCD also advocates for stormwater discharge regulation, habitat restoration, and protection of aquatic species that have been threatened by overfishing, pollution, and climate change. 

Learn more about the organization here.

8) NYC Audubon

Through advocacy, NYC Audubon supports efforts to upgrade NYC’s stormwater system. NYC Audubon also advocates for preserving natural habitat and creating green urban infrastructure in the city to reduce discharge into and subsequent damage of NYC’s watershed and wetland ecosystem water quality.

Learn more here.

9) New York City Water Trail Association (NYCWTA)

NYCWTA, a stewardship group comprising of non-motorized boating organizations in and around NYC, has conducted a water quality testing program since 2012. Volunteers collect samples from the waters in and around New York Harbor every week from May through September. The program started with 22 sample sites and grew to more than 70 sites by 2019. Their samples are tested for indicators of fecal pollution and other pathogens that could be harmful to human health.

Learn more about the organization here.

If you’re interested in collecting environmental data to measure green infrastructure effectiveness and keep your community informed, please contact us to learn how Temboo can help you!