Why Water Testing Is Important
Water testing provides objective, laboratory-verified data about your water supply. Visual inspection and temperature monitoring are important, but they cannot detect bacterial contamination, chemical contaminants, or unsafe levels of dissolved substances. Only accredited laboratory analysis can confirm whether your water is genuinely safe.
Regular testing is a legal requirement for many building types under ACOP L8 and HSG274 guidance. Even where not legally mandated, periodic testing protects building owners from liability and provides documented evidence of due diligence.
Types of Water Tests
Different situations require different types of analysis. The table below summarises the most common tests and when they are typically needed.
| Test Type | What It Measures | When Required |
|---|---|---|
| Legionella culture | Legionella bacteria (CFU/litre) | Quarterly monitoring, post-remediation |
| Total viable count (TVC) | General bacterial levels | Routine monitoring, commissioning |
| Coliform / E. coli | Faecal contamination indicators | Suspected contamination, new supplies |
| Chemical analysis | pH, chlorine, metals, hardness | Commissioning, taste/odour complaints |
| Pseudomonas | Pseudomonas aeruginosa | Healthcare, augmented care settings |
Sampling Best Practice
Accurate results depend on correct sampling technique. Samples must be collected in sterile containers provided by the laboratory, labelled correctly, and transported under controlled temperature conditions. Samples taken incorrectly can produce misleading results, leading to either false reassurance or unnecessary remediation.
For legionella sampling, it is important to collect pre-flush samples (before running the tap) to detect bacteria in the standing water, and post-flush samples to assess the general supply. Your water treatment specialist will determine the appropriate sampling points based on your system layout and risk assessment.
Understanding Your Results
Laboratory results are typically reported in colony-forming units per litre (CFU/l) for microbiological tests. For legionella, the key thresholds are: below 100 CFU/l is acceptable, 100 to 999 CFU/l requires review and possible remedial action, and 1,000 CFU/l or above requires immediate action including chlorination and resample.
Your water treatment specialist should review results with you, explain any concerns, and recommend appropriate action. Always request that results are compared against previous tests to identify trends rather than viewing each result in isolation.