Understanding Turbidity in Drinking Water and Why It Matters

You probably don’t think much about the water flowing from your tap. As long as it looks clean, tastes OK, and doesn’t smell funky, you likely assume it’s pure and safe to drink. However, a crucial but little-known factor can influence the safety of your drinking water—one you can’t measure with your senses: turbidity.

In this article, we go on a quest to clarify what turbidity is, how it affects drinking water safety, and how to reduce it in your water supply.

What Exactly is Turbidity in Drinking Water?

Add a spoonful of dirt to a glass of plain water and hold it up to the light. Can you see any fine, insoluble particles floating in the water? Or does the water seem cloudy or hazy? If so, it’s because the suspended matter scatters or absorbs light rays instead of allowing them to pass through the water. The level of clarity (or lack thereof) in the resulting liquid is called turbidity. Essentially, turbidity tells us how clear the water is.

What Makes Water “Turbid”?

If your drinking water is sourced from a river, stream, lake, or even underground—directly or indirectly, it may contain specific particulate matter that could reduce the water’s clarity.

Here are a few known culprits:

  • Sediment: When rainwater or snowmelt flows across the surrounding landscape, it picks up sediments such as clay, silt, dirt, sand, and organic matter that can enter the water and cause a spike in turbidity. Similarly, tiny particulates can leach into precipitation as the water percolates through rock and soil to underground aquifers that supply water to wells.
  • Heavy Metals: Under certain conditions, iron, manganese, aluminum, zinc, and other metals can leach from city or residential pipes and plumbing and rock and soil and enter the water passing through. These metallic elements may then bond with existing organic matter to form larger particulates that can discolor the water and increase turbidity.
  • Treatment Chemicals: As this article explains, coagulation is vital in the municipal water treatment process. In this stage, chemical coagulants like alum are added to the water to bind tiny particles together to form thick clumps called “flocs.” That way, they are easier to remove. Unfortunately, chemical residues can stay suspended if incorrect doses are used, possibly making the water hazy. In other instances, chemical disinfectants like chlorine can react with natural organic matter to form disinfection byproducts that can cause cloudiness if not filtered out.
  • Fine Organic Matter: When water passes through decaying vegetation or swampy soil, bits of leaves, plants, and biological matter may disperse into it, potentially spiking turbidity.
  • Algae and Microorganisms: When the conditions are right, bacteria, algae, viruses, protozoa, and other microbes tend to multiply and prevent sunlight from penetrating the water column. Large algal blooms may discolor the water, while excess bacteria can make it appear hazy. Most water treatment processes eliminate these microscopic organisms, but some can persist.

Why Does Turbidity in Water Matter?

Almost all drinking water treatment facilities in the U.S. measure turbidity in treated and untreated water—and for good reason.

For one, cloudiness in drinking water could mean the water is severely contaminated, potentially increasing the risk of various diseases if ingested. Elevated turbidity suggests that tiny disease-causing organisms and visible particles from the source water likely escaped the filtration process. Considerable increases in turbidity warrant additional testing for any infectious threats, thus helping to protect public health.

Furthermore, measuring and recording changes in turbidity after different stages of water treatment helps catch water quality issues early. That way, water operators can adjust chemical dosages, pH, backwash filters, slow flows, and conduct repairs to prevent unsafe water from entering the public distribution system.

Turbidity can also cause chemical disinfectants and UV light to work less efficiently, as high amounts of particulate matter provide shelter for pathogens. The rapid growth of bacteria can lead to dangerous waterborne disease outbreaks.

And let’s not forget about its potential impact on aesthetics (the water’s appearance). While some particles that increase turbidity pose a direct health threat, visible cloudiness, discoloration, or particulate residue can undermine public confidence in tap water’s safety and lead more people to buy bottled water.

As explained in this article, bottled water contain the same contaminants in tap water, cost more than investing in a water filter in the long run, increase plastic pollution, etc.

Related: Is It Safe to Drink Bottled Water Left in a Hot Car? | The Impacts of Plastic Water Bottles on Pollution & Your Wallet

How is Turbidity in Drinking Water Measured?

How turbidity is measured has come far since Italian astronomer Angelo Secchi discovered turbidity in 1865. Let’s go back to the first known turbidity measurement and track how the technology has evolved since then.

Jackson Candle Method

Back then, lab technicians used a Jackson Candle Turbidimeter to measure turbidity. This method involved placing a vertical glass tube above a burning candle. A liquid (water) was poured into the tube until the distinct image of candle flame was no longer visible to the human eye when viewed from above. The depth of the water at that point corresponded to a reading on the scale expressed in Jackson Turbidity Units (JTU). Compared to modern instruments and methods, the Jackson Candle Method resulted in inconsistencies due to differences in viewers’ eyesight and the candle used.

Portable Spectrophotometers

Researchers needed to develop a method to eliminate the subjectivity of squinting into glowing tubes associated with the Jackson Candle Method. This gave rise to handheld spectrometers. Whether in the lab or the field, these devices provide a fast and accurate way to measure turbidity in liquids. They allow you to test the water by directly immersing the tip and reading the turbidity level. They have an optical system integrating a photodiode detector with a light-emitting diode, usually LED.

The Secchi Disk

Invented by and named after Angelo Secchi in 1965, Secchi disks are also used to measure turbidity in water. They are a small, circular white disk with a black dot in the center, made from a transparent material. To measure turbidity, the Sacchi disk is lowered in the water being tested until it is no longer visible. The depth at which it disappears, known as the “Secchi depth,” is then recorded. A deeper Secchi depth suggests clearer water, while a shallower depth indicates greater turbidity.


Nowadays, portable electronic devices called “nephelometers” or turbidimeters are used to measure turbidity in water. Generally, these instruments work by shining light through a water sample and quantifying the amount of light scattered by suspended particles. The results are expressed in Nephelometric Turbidity Units (NTU). The higher the NTU, the more stuff floating in the water, and the cloudier or “thicker” it is. Lower readings indicate clearer water.

Laboratory Water Testing

While water utilities continuously monitor turbidity levels in source and treated water, lab analyses come in handy when validating online readings and ensuring regulatory compliance. Laboratory personnel use a range of modern instruments and methods to accurately pinpoint what contaminants and impurities may be hiking up your water’s turbidity levels, and other water quality issues that are worth looking into.

Learn more: 10 Common Problems a Water Test Can Detect in Tap Water

What is the Ideal Turbidity Level for Drinking Water?

The Environmental Protection Agency (EPA) regulates turbidity in drinking water across the United States. Per EPA standards, there are two key benchmarks public water systems must meet to ensure safer drinking water for consumers:

  • No more than 1 NTU at the system’s entry point. This measures the turbidity of water right before it enters the distribution system. Up to 5 NTU is temporarily allowed if it doesn’t compromise disinfection.
  • No more than 0.3 NTU in 95% of samples taken monthly from the distribution system. No single sample may exceed 1 NTU.

To put this in perspective, the Mississippi River generally ranges from 10-1,000 NTU, depending on rainfall. Effective water treatment brings those levels below EPA limits before sending water to your home’s taps.

What Happens If I Drink Water with High Turbidity?

If you fill a glass at the tap and notice the water resembles that from a pond, avoid bringing that glass anywhere near your lips—even more so if testing shows the water has high turbidity.

The cloudiness or murkiness should immediately set off alarm bells about how many microscopic elements might be lurking in the water. There could be scores of potentially dangerous contaminants floating in it, including parasites, bacteria, viruses, metals, chemicals, etc.

If you chug it down regardless, you can expect a full-scale invasion of these elements into your body, increasing your risk of various health problems. Specifically, contaminants like norovirus, rotavirus, E. coli, Salmonella, Giardia, and Cryptosporidium often mark their presence through bouts of diarrhea, vomiting, abdominal cramps, nausea, and fever in those infected. Symptoms may last several days up to two weeks without proper medical intervention.

Parasitic infections can prove life-threatening for those with weakened or underdeveloped immune systems, like infants, older folks, and immunocompromised individuals. Others may develop longer-term complications such as irritable bowel syndrome or reactive arthritis after the acute illness subsides.

Related: Glyphosate in Hard Water Linked to Kidney Disease, Study Finds | The Dangers of Chloramines in Drinking Water

How Do I Reduce Turbidity in My Drinking Water?

While your water provider is supposed to filter all the particulate matter from your city water supply, some may still slip through the water treatment process and enter your faucet, causing that distinct hazy appearance.

If your water comes from a private well and you don’t have a treatment system, you are more likely to have this problem. After all, the Environmental Protection Agency (EPA) does not regulate private wells. And bear in mind that well water travels through rock and soil to reach wells, potentially picking up dirt and other cloudiness-causing materials along the way. So, how do you reduce turbidity in your drinking water?

Whole-House Carbon Filtration

Suspended particles in water cause turbidity. Luckily, many of them can be removed through physical filtration. A multi-stage, whole-house filter system combining sediment and activated carbon filters and a UV water purifier may reduce or remove turbidity.

Here’s a brief overview of what the process looks like:

  1. Sediment Pre-Filtration: Cloudy water first passes through a sediment filter made of various materials that act like a screen mesh. These materials trap larger particles suspended in the water that contribute to the cloudiness in the water. This process removes particulates like dirt, sand, silt, clay, tiny organic materials, etc.
  2. Activated Carbon Filtration: The water then flows through an activated carbon filter. At this stage, any tinier haze-causing particles the sediment filter missed are removed. The activated carbon exerts a magnetic-like pull on the impurities and traps them in the pores of its surface area.
  3. UV Purification (Optional): A special lamp emits UV light to disinfect the filtered water. The UV light neutralizes viruses, bacteria, or parasites that might have been hiding in the source water. This ensures germs are eliminated in case particulates have sheltered them from treatment.

Learn more: Is a Whole House Water Filter Right for You? Here’s A Guide

Reverse Osmosis Filtration

Reverse osmosis (RO) filtration is another effective method to lower turbidity in water. RO water filters use a semipermeable membrane to catch particulates and other larger molecules and allowing water to pass through.

During the RO filtration process, high pressure pushes water through the membrane to remove contaminants in the following steps:

  • Prefiltration: A sediment prefilter traps large particles such as dirt, rust, sand, silt, and dust.
  • Reverse osmosis: The semipermeable membrane catches smaller, dissolved particles.
  • Discharge: The trapped contaminants are drained from the system.
  • Storage: The RO-treated water is stored for future use.

Learn more: Reverse Osmosis Water Filtration Explained | How Pre-filtration Helps Protect Reverse Osmosis Membranes

Final Thoughts

We rarely hear about turbidity in water—though our drinking water isn’t always as clear as we’d like. Often, tiny particles we can’t see individually float around, making the water appear hazy or murky, thus increasing its turbidity.

High turbidity can be dangerous because the suspended particles can hide illness-causing germs, chemicals, and other bad stuff that can make us sick. Luckily, there are ways to measure turbidity in water, including Secchi disks, turbidity meters, and handheld spectrometers. You can also purchase a water test kit and send a water sample from your tap to a certified lab for testing.

Monitoring turbidity levels in drinking water helps lower the risk of various health problems and can determine whether a filter is working as expected. Water treatment plants typically employ a range of techniques to remove turbidity from water. However, equipping your home with a whole-house activated carbon water filter (preferably with a UV water purification system add-on) or an undercounter reverse osmosis filter should help make your water clear again.