Measuring low turbidity in finished water: Which instrument is best suited for detecting low turbidity levels (nephelometric range) in potable water?

Introduction / Context:
Finished water quality targets very low turbidity to ensure effective disinfection and aesthetic acceptability. Instruments differ in measurement principle and sensitivity range.

Given Data / Assumptions:

• Low turbidity typical of post-filtration potable water.
• Need for high sensitivity and repeatability.

Concept / Approach:
The Jackson candle method is suitable for higher turbidities and is not sensitive at the low end. Turbidity tubes are crude field devices. Nephelometric (Hellige-type) turbidimeters measure light scattered at an angle and are appropriate for low turbidity monitoring in drinking water treatment.

Step-by-Step Solution:
Eliminate Jackson/tube for low ranges.Select nephelometric instrument designed for low-NTU accuracy: Hellige turbidimeter.

Verification / Alternative check:
Standards for drinking water turbidity compliance are typically based on nephelometric turbidity units (NTU), measured by nephelometers (e.g., Hellige/modern equivalents).

Why Other Options Are Wrong:

• Turbidity tube and Jackson meter lack required sensitivity for very low turbidity.
• Baylis is not the common standard for low-level compliance monitoring.

Common Pitfalls:

• Using candle method results for regulatory reporting where nephelometric methods are required.

Final Answer:
Hellige (nephelometric) turbidimeter