ISO 20761:2018

Overview

ISO 20761:2018 provides guidance for the safety evaluation of non‑potable water reuse in urban areas, focusing on water quality assessment parameters and methods. The standard is intended for reclaimed water sourced primarily from municipal wastewater (with limited industrial contribution). It covers safety evaluation across project stages - design, operation and post‑assessment - and addresses health safety, environmental safety and facilities safety. Note: potable reuse safety evaluation is outside the scope.

Key topics and requirements

ISO 20761 defines a framework and recommended parameters to evaluate reclaimed water safety and public acceptance. Major technical topics include:

• Safety framework
  • Systematic evaluation of health, environmental and facilities risks for different reuse applications.
  • Selection of parameters based on source characteristics, intended use, and local context (climatic, occupational, environmental).
• Water quality parameters
  • Routine physical/chemical: pH, BOD5, COD, TOC, ammonia, total nitrogen, phosphorus, dissolved oxygen, TDS, conductivity, alkalinity, hardness.
  • Aesthetic: colour, odour.
  • Particulate/stability: turbidity, total suspended solids (TSS), heterotrophic plate counts (HPC).
  • Disinfection and microbial indicators: residual disinfectant, chlorine demand, thermotolerant coliforms, E. coli, environmental pathogens (e.g., Legionella where relevant).
  • Toxic contaminants: specific metals (Pb, Hg, Cd), surfactants, oil/grease - selected according to source and use.
• Monitoring and criteria selection
  • Parameter selection and monitoring strategies adapted to end use (landscape irrigation, municipal non‑potable uses, environmental/recreational uses, vehicle washing, industrial uses).
  • Use of indicators or surrogates (e.g., turbidity, disinfectant residuals, bacterial indicators) for routine verification.
• Public acceptance considerations
  • Emphasis on aesthetic parameters and education to improve community acceptance of reused water.

Applications and who uses it

ISO 20761 is practical for stakeholders involved in urban water reuse programs:

• Water engineers and system designers
• Utility operators and maintenance teams
• Municipal authorities, regulators and environmental agencies
• Public health professionals and risk assessors
• Project managers, consultants and decision makers overseeing non‑potable reclaimed water schemes

It supports design decisions, operational monitoring plans, risk management, post‑implementation assessment and communication strategies to enhance public acceptance.

Related standards

• ISO 20670 (Water reuse - Terminology) is cited for consistent terminology.
• The standard was developed by ISO/TC 282 (Water reuse), Subcommittee SC 2 (Water reuse in urban areas).

ISO 20761 helps organizations implement robust water quality assessment and monitoring for safe, acceptable non‑potable reuse in urban settings, protecting human health, the environment and infrastructure while supporting sustainable urban water management.