If you’ve ever looked at a river or lake after heavy rain, you may have noticed that the water looks a little different—perhaps cloudier, darker or less clear than usual. One reason for that change is turbidity.
Turbidity is a measure of the cloudiness or haziness of water caused by tiny, suspended particles. These particles can include silt, clay, organic matter, and microorganisms.
Think of turbidity like dust in the air. Just as dust can make the air look hazy, suspended particles can make water appear cloudy.
For water utilities like Texas Water Company (TWC), turbidity is an important part of monitoring and treating water. And because it can change quickly—particularly when weather conditions affect a water source—it’s something our water treatment teams continuously manage as part of providing safe, reliable drinking water.
Turbidity can occur naturally in surface water, and the amount can change depending on what is happening in the surrounding environment.
Rainfall is one of the biggest factors. During heavy rain or flooding, runoff can carry soil, sediment, debris, and organic material into rivers, lakes, and other surface water sources. As those particles enter the water, turbidity can increase and the source water may become cloudier than normal.
That means the quality of the source water entering a treatment plant isn’t always exactly the same from one day to the next. A stretch of dry weather may produce very different source water conditions than a major storm.
Changes in turbidity don’t necessarily mean something is wrong with the water system. They do, however, affect how water needs to be treated.
It's important to remember that turbidity increases often occur in the raw water entering a treatment plant, not necessarily in the treated drinking water delivered to customers.
Not necessarily. While turbidity itself is not a contaminant, elevated turbidity can make it more difficult for treatment and disinfection processes to work effectively, which is why utilities monitor it closely.
This is an important distinction. Turbidity is a measurement of water clarity; it is not, by itself, a measurement of whether disease-causing organisms are present.
However, excessive turbidity in finished water can be an important warning sign because it may indicate that filtration or another part of the treatment process is not performing optimally. High levels of suspended particles can also interfere with effective treatment.
That’s why turbidity is closely monitored and regulated as part of the drinking water treatment process.
Turbidity is measured in Nephelometric Turbidity Units (NTU), which indicates how much light is scattered by particles suspended in water. Lower NTU values generally indicate clearer water.
You may hear turbidity mentioned in connection with a boil water notice, but the two don’t automatically go hand in hand.
A storm that temporarily increases turbidity in the water entering a treatment plant does not automatically result in a boil water notice. Treatment plants continuously monitor turbidity because sudden changes can signal that treatment processes need to be adjusted. Monitoring helps operators respond quickly to changing source water conditions.
A boil water notice may become necessary if finished-water turbidity reaches levels that indicate a significant treatment or filtration problem. Under Texas regulations, certain acute turbidity exceedances are among the conditions that require a public water system to issue a BWN. Other circumstances, such as loss of pressure, water outages, inadequate disinfectant levels or certain microbiological results, can also lead to a boil water notice.
A boil water notice is issued to protect customers when conditions indicate that the water may be unsafe for consumption or that there is a potential acute health risk.
If TWC issues a boil water notice for your area, always follow the instructions in the notice until TWC confirms that the notice has been lifted.
A boil water notice isn’t lifted simply because the original issue appears to be resolved.
According to the Texas Commission on Environmental Quality (TCEQ), the condition that caused the notice must first be corrected or determined not to pose an acute health risk. The water system must return to normal operating conditions, and required bacteriological samples must produce satisfactory results before the notice can be rescinded.
Once those requirements have been met, customers are notified that the boil water notice has been lifted and the water can again be used normally.
Turbidity isn’t something you’ll need to monitor yourself. It’s one of the many water quality and treatment conditions that trained water professionals monitor behind the scenes.
The biggest thing to remember is that changes in weather can change the water entering a treatment plant. Heavy rain, flooding, and runoff can increase sediment and other material in source water, which can make treatment more complex. TWC’s operators monitor those changing conditions, test the water and adjust treatment processes as needed.
And while turbidity can play a role in a boil water notice, an increase in source water turbidity does not automatically mean your drinking water is unsafe.
If conditions ever require customers to take precautions, TWC will communicate that information directly, including what customers should do and when normal water use can resume.
Understanding what's happening between the water source and your tap can make terms like turbidity a lot less confusing. While weather conditions can change the quality of source water from day to day, TWC's treatment professionals continuously monitor and adjust treatment processes to help ensure water delivered to customers meet state and federal drinking water standards.