Water Sampling

Commercial water sampling is the collection of water from a building’s systems and its submission to a UKAS-accredited laboratory for microbiological or chemical analysis. Sampling is taken in line with BS 7592:2022, with laboratory analysis carried out to ISO 11731 for legionella. Sampling is risk-based under ACOP L8 and HSG274 Part 2: required by the written scheme of control, after positive results, and following system works.

HSG274 Part 2 legionella action thresholds. Below 100 cfu/L: system under control, continue monitoring. 100 to 1,000 cfu/L: review the control scheme and resample. Above 1,000 cfu/L: immediate remedial action required.

General bacteriological analysis

Broader microbiological screening can identify E. coli, total coliforms, Total Viable Counts (TVC), Pseudomonas aeruginosa, and Enterococci depending on the parameters specified. Pseudomonas aeruginosa sampling is a particular requirement in healthcare and augmented care environments under HTM 04-01 Part C and BS 8580-2:2022; it is less commonly required in standard commercial premises.

Chemical analysis

Chemical parameters including pH, hardness, dissolved oxygen, chlorine residual, total dissolved solids, and metals such as iron, copper, and lead can be tested where the written scheme of control requires it. Chemical analysis is common on closed heating and cooling systems, process water, and buildings with older or mixed-metal pipework.

Where are water samples taken?

Sample points are identified by the legionella risk assessment and documented in the written scheme of control. Typical locations under HSG274 Part 2 include:

• Hot water sentinel outlets: the taps nearest to and furthest from the calorifier or hot water source
• Cold water sentinel outlets: the taps nearest to and furthest from the cold water storage tank or mains entry
• Return loops on circulating hot water systems
• Hot water calorifiers and storage cylinders
• Cold water storage tanks
• Thermostatic mixing valves (TMVs) and other risk outlets, where called for
• The incoming mains supply where the written scheme requires it

For buildings with multiple zones, complex distribution loops, or known problem branches, additional sample points are typically added to give a representative picture of system performance.

When water sampling is required

Water sampling is risk-based: it is required when the written scheme of control specifies it, or when a triggering event occurs. Common triggers include:

Where the written scheme of control specifies it

The written scheme produced following a legionella risk assessment sets out which points are sampled, at what frequency, and what the action thresholds are. Higher-risk buildings, those with known control issues, or those serving vulnerable users are more likely to have sampling built into the scheme as a routine activity.

When temperature controls cannot be maintained

If hot water temperatures persistently fall below the 50°C target at outlets, or cold water rises above 20°C, microbiological sampling is the next line of evidence under HSG274 Part 2 

New water mains commissioning

When a new water main is brought into service, sampling is required to confirm the water is safe before use. This links closely to the water chlorination certificate process.

Post-incident retesting

Following a positive legionella result, a system disinfection, or a significant change to a water system, sampling is required to verify the issue has been resolved before the system returns to normal use. This often follows legionella control works or water tank cleaning.

Higher-risk premises

Healthcare premises under HTM 04-01, care homes, and other settings serving vulnerable users are subject to additional sampling expectations, including routine Pseudomonas aeruginosa sampling in augmented care areas.

Insurance and compliance audit

Insurers, local authorities, and landlords increasingly request documented water sampling records as evidence that statutory obligations are being met. Sampling records form part of a defensible water safety file.

How the water sampling process works

We agree the sample points with you based on your existing risk assessment and written scheme of control, or advise on appropriate locations if no scheme is in place.

A specialist water hygiene operative attends your premises and collects samples in line with BS 7592:2022. The initial collection typically takes less than an hour on most sites; larger or multi-site buildings take longer.

Samples are transported to a UKAS-accredited laboratory and submitted for analysis to BS EN ISO 11731:2017 for legionella, and equivalent standard methods for other parameters.

Bacteriological results are returned within 3 to 5 working days. Legionella culture results take 10 to 14 working days, because the bacteria require extended incubation. You receive a written report covering all parameters tested.

Where a result exceeds action thresholds, we advise on next steps. Depending on the finding, this may include flushing, outlet disinfection, a full system clean, or further investigation. Remedial works are managed through our quoted works process.

How we can support you

Water sampling is available as part of a PPM and compliance contract or as a standalone service through quoted works.

For buildings with an ongoing monitoring requirement under a written scheme of control, a PPM contract is the most straightforward arrangement. We build the sampling schedule into your planned maintenance programme and coordinate attendance without you having to prompt us each time. Contract customers also receive priority response and preferential rates.

For one-off requirements, post-incident retesting, or new mains commissioning, we quote for the sampling visit and laboratory analysis as a fixed, itemised cost. If remedial works are identified, these are managed separately through the same quoted works route.