Overview
EN ISO 7027-1:2016 - "Water quality - Determination of turbidity - Part 1: Quantitative methods" (CEN adoption of ISO 7027-1:2016) defines two standardized optical methods for quantitative turbidity measurement in water using optical turbidimeters and nephelometers. It covers instrument principles, sampling and sample handling, apparatus and reagents, calibration with standards (formazin), measurement procedures, expression of results and reporting. The standard distinguishes nephelometry (diffuse-scatter measurement, low turbidity) and turbidimetry (attenuation measurement, high turbidity), and provides guidance to minimize interference from dissolved colour and air bubbles.
Key topics and requirements
- Two measurement methods
- Nephelometry: measures diffuse radiation; suitable for low-turbidity waters (e.g., drinking water). Results in nephelometric turbidity units (NTU). Typical range: <0.05 NTU to 400 NTU (instrument-dependent). NTU is numerically equivalent to Formazin Nephelometric Unit (FNU).
- Turbidimetry: measures attenuation of transmitted radiant flux; suited to highly turbid waters (e.g., waste waters). Results in formazin attenuation units (FAU). Typical range: 40 FAU to 4 000 FAU.
- Sampling and sample handling
- Use scrupulously clean glass or plastic containers (acid or surfactant cleaned).
- Analyze as soon as possible; if stored, keep cool and dark and measure within 24 hours. Allow samples to reach room temperature and avoid air contact.
- Interferences and mitigation
- Dissolved light-absorbing substances (colour) can bias measurements - measurement at wavelengths >800 nm reduces colour interference.
- Air bubbles can affect results; careful handling and sample preparation are required.
- Calibration and standards
- Use formazin-based calibration materials; Annex A evaluates suitability of alternative polymers as secondary standards.
- Instrument parameters
- Measurement depends on wavelength, detector angle, and aperture; consistent instrument use and adherence to the standard are needed for instrument-to-instrument comparability.
Applications and users
- Water utilities performing drinking water quality monitoring.
- Wastewater and industrial discharge monitoring where high turbidity occurs.
- Environmental laboratories, regulatory bodies and field labs conducting compliance testing.
- Instrument manufacturers and test method developers validating and calibrating nephelometers and turbidimeters.
- Researchers studying suspended solids, water clarity, and treatment efficacy.
Related standards
- ISO 7027 (general series) - Part 2 (semi-quantitative methods) is under preparation.
- EN ISO 7027-1:2016 supersedes earlier versions (EN ISO 7027:1999) and is the CEN-endorsed text for Europe.
Keywords: EN ISO 7027-1:2016, turbidity measurement, nephelometry, turbidimetry, NTU, FAU, water quality, optical turbidimeters, formazin.