7.4 Sampling, Quality Assurance and Audit

7.4 Sampling, Quality Assurance and Audit

Why "ensuring quality" sits in a hygiene course

The final unit of the 2023 National Water Hygiene e-Learning programme is ensuring quality: sampling and audit. Everything in the earlier units describes how to prevent contamination. This unit explains how the industry proves that prevention worked. Hygiene on the water network is never simply assumed: water samples verify the quality of the water, and audits verify the people, cards and procedures behind it.

For a card-holder, that has three practical consequences. You may be asked to take or support samples, so you must not be the cause of a false result. Your work may be held back until sample results are satisfactory, so you need to understand why. And you, your card and your methods can be audited at any time.

What a water sample tells you

Water companies test drinking water against the standards in the Water Supply (Water Quality) Regulations 2016. The microbiological standard for E. coli and coliform bacteria in treated water is zero per 100 ml. These bacteria are indicator organisms: their presence shows that a pathway exists for faecal or environmental contamination, even if no pathogen has yet been found (Section 2.3).

Routine regulatory monitoring takes place at three main points:

• water leaving treatment works, to confirm treatment and disinfection;
• service reservoirs and water towers, which must be monitored weekly while in supply for bacteriological indicators and chlorine residual;
• customers' taps, to confirm the water is still wholesome at the point of use.

The results are reported to the Drinking Water Inspectorate. In 2025 the DWI recorded 49 coliform compliance failures at treatment works and 65 at service reservoirs, with three E. coli detections at treatment works and four at service reservoirs, out of 3,632,669 microbiological tests in England. It identified ingress into contact tanks, treated water tanks and service reservoirs as a recurrent risk. Rare failures are still investigated as possible routes for contamination.

Sampling after work on the network

Water UK's technical guidance notes link sampling to the job that has just been done:

A failed sample is never just paperwork. After a repair, Water UK's guidance expects the main to be re-sampled, extra samples taken in the surrounding network and further action considered, including disinfection or protective advice to customers.

Sample points and hygienic sampling

A sample is only as good as the tap it came from. Water UK's TGN 15 sets out good practice for sample points at treatment works and service reservoirs:

• sample taps of hygienic design, with no attachments or inserts, kept clean and free of anything that could affect the microbiological result;
• short sample lines in good condition, dedicated to treated water, with no T-junctions where water could stagnate;
• secure locations, protected from the weather, vandalism and environmental contamination, with drainage so the area cannot flood;
• flame disinfection of a tap only where there are no flammable materials or fumes nearby;
• periodic cleaning, disinfection and flushing of sample points by trained staff, and inspection for damage that could let in water or vermin.

Anyone working around treated or partially treated drinking water at a sample point must also meet the TGN 1 medical screening requirements. A careless sample can do harm in two directions: it can produce a false failure that triggers an unnecessary investigation, or it can hide a real problem. Clean hands and gloves, a clean tap, and following the sampling method exactly are part of water hygiene, not an extra.

Audit: checking people, cards and procedures

Water UK's Principles of Water Supply Hygiene are direct about the human side of quality assurance:

• Cards must be carried at all times by anyone working on Restricted Operations.
• Regular audits are recommended to confirm that everyone working on Restricted Operations holds a valid card.
• Anyone who cannot produce a valid card should be suspended from Restricted Operations.
• People who flagrantly or repeatedly breach hygiene standards should be suspended from Restricted Operations, and their authorisation may be revoked while they are retrained.

Water UK's medical screening note adds that undertakers should have procedures to make sure everyone on Restricted Operations, including contractors, complies with the approved hygiene scheme. Audits therefore check more than cards: they look at tools, vehicles, materials storage, disinfection records and whether the method on site matches the method on paper.

Records matter for a second reason. Section 70 of the Water Industry Act 1991 gives a defence to anyone who took all reasonable steps and exercised all due diligence (Section 1.2). Disinfection records, sample results and signed method statements are how a company, or an individual, shows that diligence after the event.

Site scenario: the sample that failed

A new main on a housing development has been disinfected, flushed and recharged, and the samples are taken. One result shows coliform bacteria. The main is not connected. The crew's records are checked to see how the pipe was stored and laid, and whether any end was left uncapped. In line with the undertaker's procedure, the main is flushed, re-chlorinated and sampled again, and it is connected only when documented results are satisfactory. If the next batch of pipes is stored off the ground with end caps in place, the failure has done its job: it has caught a problem before any customer drank the water.

Common candidate traps

• "Sampling is the laboratory's job, not mine." The laboratory analyses the sample, but the result depends on how the work was done and how the sample was taken.
• "Clear water means a pass." Coliforms and E. coli are invisible. Only a satisfactory laboratory result shows that the microbiological standard is met.
• "Card checks only happen at induction." Water UK recommends regular audits, and anyone who cannot produce a valid card should be suspended from Restricted Operations.