The Ultimate Guide to Turbidity and Turbidimeters

Person drinking water from a glass

The Ultimate Guide to Turbidity and Turbidimeters

Water covers about 70% of the Earth’s surface. But only 2.5% of all the water in the world is fresh. That makes water the most abundant, yet precious resource we have. Understanding how to track and treat freshwater is critical to human health. Turbidity is a major component of monitoring water quality.

But what exactly is turbidity? If you’ve ever gone swimming in a lake or river, you understand the concept of turbidity. You just didn’t realize it at the time.

The Definition of Turbidity

Turbidity is a measure of water clarity that applies to all types of water. It’s used to determine the cloudiness of water. The more cloudy the water, the more turbid. And the more turbid the water, the more likely you’ll get sick from drinking or bathing in it. Haze, as it’s often called, comes from particles suspended within the water. Certain particles are large enough that they settle quickly.

Smaller particles, or colloidal particles, might never settle. They pose the greatest risk to water quality. Turbidity can also be used to describe other substances, like plastics or glass. But for this article, we’re focusing on water.

A Brief History of Water Quality

In the ancient world, people used their senses to test water quality. Measurements included how the water looked and tasted. Romans brought fresh water into their cities through aqueducts. They understood the importance of protecting against water-borne diseases. Through the years, people adopted crude methods of filtration and boiling to help improve water quality. People soon realized that wastewater must be properly disposed of to improve health conditions. The first sewer systems were established in Britain in the 18th century. The scientific study of water quality has been around since the early 1900’s. In 1908, Jersey City, New Jersey became the first U.S. city to treat drinking water.

In the 1970’s legislation passed through Congress to set standards for drinking water quality throughout the U.S.

Water Quality and Turbidity

In the U.S., the Environmental Protection Agency (EPA) approves water quality standards. Factors vary from state to state.

Some of the most common factors include:

  • Acidity or pH
  • Color
  • Oxygen levels
  • Turbidity

Turbidity is often removed in treatment plants. They use sand filtration and settling tanks to lower the overall amount. There are also certain chemicals that lower amounts through chemical reactions. Levels change often and it’s important to continually monitor water clarity to ensure safe levels for drinking or recreational use.

Causes of Turbidity Changes

Turbidity is affected by a variety of factors, both natural and man-made. Particles found in water can be any combination of silt, dirt, bacteria, or chemicals. Agriculture is a common culprit. When farmers irrigate their fields, runoff causes abnormally cloudy water. Construction and mining areas have the same problem.

In open water, turbidity is influenced by phytoplankton and algae. In certain environments, high amount supports plants and animals that need low levels of light.

The Importance

Water quality is one of the leading health issues facing the world today. Many people around the planet don’t have access to clean drinking water. The higher the turbidity of a water source, the more likely it is to make people sick. Bacteria and viruses cling to the particles in water and can hide behind particles during treatment.

During rainy seasons, runoff into streams and rivers makes turbidity higher. When water treatment plants have to deal with more turbid water, they tend to have more mud and silt in their systems. Filters and pipes can become clogged. Strict measurement of turbidity throughout the treatment process can be critical to keeping water standards reasonable.

Levels are also important for environmental standards. When water sources are contaminated with agricultural runoff, the fish and water plants suffer. Cloudier water allows less light to reach the bottom. Less light means the native plant species can’t grow like they normally would. This affects the entire food chain.

Measurements and Standards

The primary unit of turbidity measurement is a Nephelometric Turbidity Unit or NTU. This method measures how light scatters off the particles suspended in the water. NTUs are most often associated with ratings of drinking water.

The World Health Organization (WHO) states that drinking water should never be above 5.0 NTU.

Another way to measure water clarity is with a Secchi disk. The Secchi disk is a black and white disk that is lowered into a deep body of water. When the disk is no longer visible, it’s measured in meters or centimeters. The Secchi disk is ideal for quick, water quality field tests of lakes and deep rivers.

The Turbidimeter

Turbidimeters measure the density of particles in the water. Beams of light shoot through the water. The intensity of the light scattering is measured to give a reading of turbidity. Turbidimeters and other similar instruments are commonly used in water treatment plants to monitor turbidity throughout the treatment process.

If the amount measures exceed normal levels at any point in the filtration process, the plant knows where to look for the problem. Turbidimeters also help state and local governments know when water is safe for recreation. Beaches, lakes, and rivers are closed to the public if the amount increases to unsafe levels.

Our Most Precious Resource

Almost 60% of your body is water. Environmental toxins in your drinking water can have a huge impact on your health.

The study of turbidity is one of the most important factors in safe drinking water. Using turbidimeters, government and regulatory agencies make sure water is safe for all Americans. If you are interested in testing the quality of your own water, there are at-home kits available from many major retailers. These kits test temperature, pH, turbidity and oxygen levels in your water.

Check out some of our other blog articles for more innovative solutions to your measurement and control needs.

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