A Comprehensive Exploration of ISO 6222:1999 - Enumeration of Culturable Microorganisms in Water Quality Assessment

January 24, 2024 by
A Comprehensive Exploration of ISO 6222:1999 - Enumeration of Culturable Microorganisms in Water Quality Assessment
Kadesha Dawkins


In the realm of water quality assessment, ISO 6222:1999 stands as a beacon, providing a meticulous procedure for the enumeration of culturable microorganisms. These microorganisms, acting as microbiological markers, offer valuable insights into the health and safety of water resources. This comprehensive exploration unveils the significance, objectives, methodology, and applications encompassed within this ISO standard.

Significance of Microbiological Markers

Microorganisms exhibiting behavior analogous to pathogens play a pivotal role in water quality assessment. Their behavior, origin, concentration, and reactions to external factors mirror those of pathogenic microorganisms. The identification and quantification of these markers through diversity indices contribute to a holistic understanding of water quality, complementing physicochemical analyses.

Objectives of Enumeration

The ISO 6222:1999 procedure focuses on the identification and enumeration of aerobic and mesophilic microorganisms. The objectives include:

  • Assessment of water resource status at their source.
  • Determination of treatment process efficacy for water intended for human consumption.
  • Establishment of cleanliness levels and conditions within distribution systems.
  • Detection of anomalous changes in microorganism numbers within the distribution network.

Guiding Bibliography

The procedural framework is anchored by ISO 6222:1999, a guiding document that standardizes the enumeration of culturable microorganisms. The methodology outlined ensures consistency and reliability in water quality assessments.

Sample Preparation in Accordance

 The procedure begins with meticulous sample preparation following ISO 8199 standards, setting the stage for accurate and representative analyses.

Pour Plate Technique

 Utilizing the pour plate technique, 2 ml of the prepared sample is combined with 15/20 ml of Yeast Extract Agar (YEA) (CAT. 1049). This step serves as a crucial initiation, promoting the growth of culturable microorganisms.

Incubation Series 1 and 2

 Incubation becomes a key phase, with Series 1 conducted at 36 ± 2 ºC for 44 ± 4 h, and Series 2 at 22 ± 2 ºC for 68 ± 4 h. These incubation conditions foster optimal growth, allowing for a comprehensive assessment of microorganism colonies.

Enumeration and Expression

Post-incubation, meticulous counting is performed in each series of plates. The results are expressed as Colony-Forming Units per milliliter (CFU/ml), providing a quantitative measure of culturable microorganisms.


 ISO 6222:1999 emerges not just as a standard but as a comprehensive methodology for water quality assessment. Its application ensures a nuanced understanding of microbial dynamics in water resources, treatment processes, and distribution networks, serving as a cornerstone for water management authorities and ensuring the provision of safe and high-quality water for diverse purposes.

Yeast Extract Agar 1049

REST Client (Huachao Mao)