ISO 19458:2006

Overview

ISO 19458:2006 - Water quality - Sampling for microbiological analysis provides practical guidance for planning and performing water sampling for microbiological investigations. The standard covers design of sampling regimes, selection of representative sampling points, aseptic sampling techniques, and the transport, handling and storage of samples until analysis begins. It is intended to ensure that samples received by the laboratory accurately reflect the microbiological quality of the water source.

Key topics and technical requirements

• Sampling planning: Guidance on defining objectives (compliance, contamination characterization, source identification) and determining sample number and frequency (see Annex A for statistical considerations).
• Sampling point selection: Choose locations that account for vertical, horizontal and temporal variability; avoid unstable points and consider hydraulic heterogeneity.
• Personnel competence: Formal training and documented competence for staff performing sampling.
• Sample containers and volumes:
  • Use clean, sterile bottles for routine sampling (commonly 500 ml for multiple assays; larger volumes for Legionella, viruses, protozoa).
  • Bottle materials: glass (reusable) or plastics (polyethylene disposable); consider surface adhesion effects.
• Sterilization:
  • Autoclave at (121 ± 3) °C for ≥15 min; dry-oven option at (170 ± 10) °C for ≥1 h.
  • Commercially supplied sterile bottles should have sterilization certificates; batch sterility checks recommended.
• Inactivation of disinfectants:
  • Use reducing agents (e.g., sodium thiosulfate). The standard gives dosing guidance (theoretical mass: 7.1 mg sodium thiosulfate pentahydrate per 1 mg chlorine; 0.1 ml of prepared solution per 100 ml bottle commonly used).
• Quality control of bottles: Methods for sterility testing (roll-bottle or broth incubation), checking for residual disinfectant and assessing container toxicity.
• Transport and storage: Procedures and recommended maximum holding times/temperatures are provided (see Annex B for detailed recommended/acceptable values).

Practical applications and users

ISO 19458 is used by:

• Water utilities and distribution system managers performing routine compliance or contamination investigations
• Environmental and public health laboratories preparing and verifying microbiological samples
• Consultants, researchers and field teams sampling surface water, drinking water, recreational waters and cooling systems
• Pool operators and building managers conducting Legionella or disinfection efficacy assessments

Adopting ISO 19458 helps ensure representative sampling, preserves microbial integrity during transport, and supports defensible laboratory results.

Related standards

• ISO 5667 series (sampling design, techniques and preservation) - referenced repeatedly for broader sampling context.
• Laboratory-specific microbiological test standards (as applicable).

Keywords: ISO 19458, water quality, sampling for microbiological analysis, sample containers, sterilization, sodium thiosulfate, sampling point, ISO 5667.