Overview
ISO 13647:2026 - Water quality - Enumeration of culturable microorganisms - Colony count by spread plate inoculation on R2A medium is an international standard published by the International Organization for Standardization (ISO). This document outlines a reliable method for detecting and enumerating culturable microorganisms present in various water types. It employs the colony count technique using Reasoner’s 2 Agar (R2A) medium and a spread plate inoculation, followed by incubation at 22°C for seven days. The standard is applicable to water intended for human consumption, including:
- Water from public drinking water treatment processes
- Bottled water
- Well water intended for consumption
- Chlorinated and non-chlorinated tap water in distribution systems and containers
The standard also allows for adaptation to other water matrices, provided that appropriate performance validation is conducted by the laboratory.
Key Topics
1. Principle of the Method
- Spread plate technique on a low-nutrient R2A medium
- Incubation at 22°C for 7 days
- Enumeration of visible colonies as culturable microorganisms
2. Applicability & Scope
- Designed for a wide range of waters, especially those with low microbial content
- Enables monitoring of water treatment efficacy and distribution system cleanliness
3. Sampling, Storage, and Quality Assurance
- Strict sampling and transport protocols (ISO 19458 & ISO 5667-5)
- Samples must be cold-stored and analyzed within 24 hours of collection
- Laboratories must implement quality control systems, use control strains, and verify media performance
4. Expression and Reporting of Results
- Results reported in colony forming units per millilitre (cfu/ml)
- Clear guidelines for test reporting and documentation
5. Use of Standardized Media and Equipment
- Specifications for preparation and performance testing of R2A agar
- Recommendations for laboratory equipment and handling procedures
Applications
The ISO 13647:2026 standard provides practical value to water testing laboratories, public health authorities, and utilities by:
- Routine Monitoring: Assessing microbial presence in municipal drinking water, bottled water, and well water supplies
- Process Control: Evaluating the efficiency of water treatment processes and monitoring for potential contamination or treatment failures
- Distribution System Surveillance: Detecting subtle changes in microbial population that may indicate biofilm growth or breaches in water system integrity
- Regulatory Compliance: Supporting regulatory requirements for water microbiological quality by providing a standardized and reproducible testing method
- Comparative Analysis: Facilitating comparison between water samples by using a harmonized method
The longer incubation period and lower nutrient content of R2A medium, as specified in this standard, make it particularly suitable for detecting a broader spectrum of culturable microorganisms, including slow-growing bacteria that are often missed by traditional nutrient-rich media.
Related Standards
For comprehensive water quality assessment and laboratory best practices, users should be familiar with the following related ISO standards:
- ISO 6222: Water quality - Enumeration of culturable micro-organisms - Colony count by inoculation in a nutrient agar culture medium
- ISO 8199: Water quality - General requirements and guidance for microbiological examinations by culture
- ISO 11133: Microbiology of food, animal feed and water - Preparation, production, storage and performance testing of culture media
- ISO 19458: Water quality - Sampling for microbiological analysis
- ISO 5667-5: Water quality - Sampling - Part 5: Guidance on sampling of drinking water from treatment works and piped distribution systems
- ISO 29201: Water quality - The variability of test results and the uncertainty of measurement of microbiological enumeration methods
Adopting ISO 13647:2026 ensures high standards of rigor and consistency in water microbiological testing, providing confidence in the safety of water intended for human use and supporting public health protection.
Open preview (PDF)Water quality — Enumeration of culturable microorganisms — Colony count by spread plate inoculation on R2A medium