How to Choose a Turbidity Meter for Water Treatment Plants: A Stable and Reliable Low-Turbidity Online Monitoring Solution

Turbidity is one of the most intuitive sensory indicators of drinking water quality, directly affecting water clarity, taste, and consumer confidence. Finished water turbidity is not only a barometer of treatment process performance in water treatment plants, but also the final safeguard for drinking water safety. According to the current Standards for Drinking Water Quality (GB5749-2022), the turbidity limit for finished water is ≤ 1 NTU. Many advanced water plants have set internal control targets at 0.5 NTU or even below 0.1 NTU. This places stringent demands on turbidity monitoring equipment, requiring ultra-low detection limits, high repeatability, and long-term stability, especially at critical points such as finished water outlets, secondary water supply systems, and distribution network endpoints.

Traditional portable or laboratory turbidity meters struggle to meet continuous online monitoring requirements. Modern water treatment plants therefore increasingly favor online turbidity meters based on the 90° nephelometric method. This approach simulates human visual perception of light scattering, offering high sensitivity and strong anti-interference performance, and has become the mainstream technology for drinking water monitoring. Nexisense turbidity sensors are specifically optimized for low-turbidity applications, integrating self-cleaning mechanisms, optical path compensation, and digital outputs. They perform exceptionally well in real-world operation, helping water plants achieve refined management and regulatory compliance.

What Is Turbidity and Why Is Finished Water Turbidity So Critical?

Turbidity is measured in NTU (Nephelometric Turbidity Unit) and quantifies the degree of light scattering caused by suspended particles, colloids, and fine organic or inorganic matter in water. By standard definition, the light scattering produced by 1 mg of SiO₂ in 1 liter of water corresponds to 1 NTU. Higher turbidity indicates murkier water, while lower turbidity indicates clearer water.

In drinking water, high turbidity not only affects appearance and taste but also conceals potential risks. Suspended solids can adsorb pathogens, heavy metals, and organic pollutants, reducing disinfection efficiency (such as chlorination) and increasing the risk of microbial regrowth. At the same time, turbidity fluctuations reflect abnormalities in coagulation, sedimentation, and filtration processes, potentially signaling microbial contamination risks in finished water. As a result, water plants treat finished water turbidity as a core internal control indicator. Real-time monitoring enables timely adjustment of chemical dosing, filtration rates, and backwash cycles, ensuring stable and compliant water supply.

The 90° Nephelometric Method: The Gold Standard for Low-Turbidity Monitoring

The 90° nephelometric method is an internationally recognized approach for drinking water turbidity measurement, compliant with EPA 180.1 and ISO 7027 standards. The principle involves directing infrared or white light into a water sample; suspended particles scatter the light, and a photodetector positioned at 90° captures the scattered light intensity. The scattered light is positively correlated with particle concentration and is converted into NTU values through signal processing algorithms.

Compared with other methods—such as transmission methods that are susceptible to color interference or forward-scattering methods that are more sensitive to larger particles—the 90° nephelometric method provides excellent linearity and repeatability in the low-turbidity range of 0–5 NTU. It is particularly suitable for finished water monitoring. Nexisense sensors utilize proprietary optical paths and detector structures, combined with real-time compensation algorithms, to further suppress the effects of air bubbles, temperature variations, and light source drift, achieving sub-0.01 NTU resolution.

Key Selection Criteria for Turbidity Meters in Water Treatment Plants

When selecting a turbidity meter, the following core performance aspects should be considered:

• Ultra-low detection limit and high accuracy: With finished water targets below 0.1 NTU, instruments must achieve errors of less than ±0.02 NTU or ±2% of reading in the 0–1 NTU range.

• Long-term stability: Optical windows are prone to fouling and drift; self-cleaning mechanisms (such as wipers or air purging) are essential.

• Maintenance-free design: Minimizes manual intervention and supports 24/7 water plant operation.

• Digital integration: RS485-Modbus communication supports cloud platforms, mobile access, and seamless SCADA integration.

• Multi-scenario adaptability: Reliable performance from raw water to finished water and distribution network endpoints.

Nexisense online turbidity analyzers are specifically optimized for drinking water applications and incorporate all of these features. In practical use, they significantly extend maintenance intervals while delivering highly reliable data.

Technical Highlights of Nexisense Turbidity Sensors

Nexisense turbidity sensors offer several advanced technical advantages:

• Standard 90° nephelometric measurement with proprietary bubble-filtering and flow-stabilizing structures to ensure stable sampling conditions.

• Built-in automatic cleaning wipers that periodically remove deposits from optical windows, preventing biofilm formation and particle accumulation, ideal for long-term submersible installation.

• Real-time algorithmic compensation for turbidity, temperature, and other interferences, with a measurement range of 0–100 NTU optimized for low-turbidity performance, suitable for finished water, secondary water supply, membrane filtration systems, and swimming pools.

• Digital output via RS485 interface and Modbus protocol for easy integration into existing systems, with optional cloud-based remote monitoring to track trends anytime.

• Low power consumption and water-saving design with minimal sample flow, reducing operational costs.

These features enable outstanding performance in finished water monitoring. Many users report minimal drift and timely alarms, allowing rapid response to process fluctuations.

Practical Application Scenarios and Value

• Finished water monitoring: Real-time assessment of filtration performance, guiding backwash timing and preventing turbidity exceedances.

• Distribution network endpoints: Detection of secondary contamination or turbidity increases caused by aging pipelines.

• Direct drinking water and membrane treatment: Verification of ultrafiltration or nanofiltration performance to ensure turbidity below 0.1 NTU.

• Swimming pools and surface water: Supporting disinfection control and ecological assessment.

In real deployments, Nexisense sensors have helped multiple water treatment plants stabilize average finished water turbidity below 0.2 NTU, enhancing supply quality and user satisfaction.

Frequently Asked Questions

Why must water treatment plants choose low-turbidity-specific meters?
Finished water targets are often below 0.5 NTU. Standard turbidity meters lack sufficient resolution and stability at low ranges, making them unable to meet GB5749-2022 requirements.

Is self-cleaning functionality truly necessary?
Optical window fouling is the primary source of error in low-turbidity measurement. Self-cleaning can reduce maintenance frequency from weekly to monthly, significantly lowering labor costs.

How can instrument accuracy be verified?
Regular verification using standard formazin solutions, combined with trend analysis of process data, helps confirm measurement consistency.

Does sensor installation location matter?
It is recommended to install sensors on finished water main pipelines or downstream of pressure-stabilizing tanks to ensure stable flow and minimize air bubble interference.

Conclusion: Choosing the Right Turbidity Meter to Safeguard Every Drop of Clean Water

Although turbidity is a sensory indicator, it carries the core responsibility of drinking water safety. In an era where finished water control targets reach 0.1 NTU, stable and reliable online turbidity monitoring has become a standard configuration for water treatment plants. Modern sensors combining the 90° nephelometric method with self-cleaning and intelligent compensation technologies—such as Nexisense products—are enabling refined operations through high precision and low maintenance. Choosing the right equipment not only ensures regulatory compliance but also enhances water supply quality, giving consumers confidence in every glass of water. In the future, water quality monitoring will become increasingly intelligent and integrated, jointly safeguarding the lifeline of our cities.