Abbreviation for “Formazine Nephelometric Unit”. Calibration unit in compliance with standard ISO 7027 for turbidity measurement using the scattered light method. Based on a formazine solution. Calibration (turbidity)
Typical turbidity values for water | FNU |
---|---|
Limit in Central Europe | 1 |
Targeted by most waterworks | 0.1 |
Guideline WTO (ideal) | < 5 (< 1) |
Raw water* | < 0.5 |
After flocculation and filtration* | < 0.2 |
Subject to the source of Raw water its turbidity can and does very greatly, for instance river water extracted for use in a water treatment plant can easily reach 200FNU and greater.