Technical Information: Selection of Suitable Water for Food Microbial Testing

ISO 11133 explains the recommended water quality for the preparation of culture media for food microbiological testing.

To ensure accurate results, prevent false positives or false negatives, and avoid contamination, it is essential to carefully select reagents containing water when preparing liquid or solid media. Tap water may contain various impurities that can affect bacterial growth or cause errors in the prepared media. Since water is a major component of the media, the removal of these contaminants from water is crucial for media preparation. The recommended water quality for media preparation is detailed in ISO 11133:2014 ("Microbiology of food, animal feed and water — Preparation, production, storage and performance testing of culture media"). Additionally, ANNEX H discusses troubleshooting for media, citing the use of inappropriate quality of pure water as a cause of incorrect pH, color anomalies, formation of precipitates, and culture inhibition. This technical document explains the ISO 11133 standards and Merck's pure water production systems that meet these criteria.

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