Overview
EN ISO 7027-2:2019 - Water quality - Determination of turbidity - Part 2 - specifies semi-quantitative methods to assess water transparency. Published by CEN/ISO, it complements ISO 7027-1 (quantitative turbidity measurement) and is intended for laboratory and in‑situ (field) use. The standard covers three main approaches: the transparency testing tube, the transparency (Secchi‑type) testing disc, and diver visibility assessments, and provides guidance on sampling, apparatus and expression of results.
Key topics and technical requirements
- Scope and purpose: Procedures for semi‑quantitative assessment of transparency of surface waters, bathing waters, wastewater and marine environments.
- Methods covered:
- Transparency testing tube (laboratory or close‑to‑site): specifies apparatus dimensions (glass tube ~600 mm ±10 mm length, internal diameter ~25 mm ±1 mm, graduations 10 mm), shielding, test print or mark and constant light source requirements for visual range measurement.
- Transparency testing disc (field/Secchi‑type): measurement of visual range in upper water layers; widely used in surface, bathing and marine monitoring.
- Diver visibility: standardised approach for estimating visibility at designated depths by trained divers.
- Sampling and sample handling: Clean sample bottles, bubble‑free filling and prompt measurement; cleaning recommendations (e.g., acid or surfactant) are referenced.
- Data expression and reporting: Procedures for expressing visual range and transparency results, including notes on estimating the attenuation coefficient (useful in marine monitoring).
- Quality and validation: References to interlaboratory field study results (Annex B) and normative references such as CIE S 017 for lighting vocabulary.
- Limitations and interferences: Notes that dissolved colouring substances and surface reflections (wind/light conditions) can affect results.
Practical applications and users
- Environmental monitoring teams performing water quality and turbidity surveys.
- Laboratories needing a semi‑quantitative alternative to nephelometric/optical turbidimeter methods.
- Marine and limnology researchers using Secchi‑type data to estimate light penetration and trophic conditions.
- Bathing water and wastewater managers for routine transparency checks.
- Diving teams and monitoring programs that assess underwater visibility for ecological surveys or safety.
Related standards
- ISO 7027-1:2016 - Quantitative methods using optical turbidimeters and nephelometers (complements Part 2).
- CIE S 017/E - International lighting vocabulary (normative reference used in the standard).
EN ISO 7027-2:2019 is a practical standard for organisations that need repeatable, field‑capable transparency assessments to inform water quality management, ecological studies and regulatory monitoring. Keywords: EN ISO 7027-2:2019, turbidity, transparency testing tube, Secchi disc, water quality monitoring, attenuation coefficient, semi-quantitative methods.
