PWTAG Water Testing Requirements: What UK Pool Engineers Must Know

PWTAG — the Pool Water Treatment Advisory Group — sets the water quality standards that UK pool operators are expected to follow. Their guidelines aren't legislation in themselves, but they're treated as the benchmark of good practice. Local authorities and the HSE reference PWTAG standards when investigating complaints or incidents, and courts have used them as the measure of reasonable care.

If you're a pool service engineer working on commercial, shared-use, or holiday-let pools, Following PWTAG guidance isn't just best practice — it's what your clients expect you to deliver. Here's what the guidelines require and how it affects your day-to-day work.

Who PWTAG Applies To

PWTAG standards apply to all pools and spas accessible to the public or to paying guests. This includes:

• Hotel and leisure centre pools
• Holiday park and caravan site pools
• Holiday rental properties with pools or hot tubs
• School and university pools
• Hydrotherapy pools
• Gym and health club pools
• Shared residential pools (apartment complexes, housing developments)

Private domestic pools used solely by the homeowner aren't covered by PWTAG. However, many service engineers apply the same standards to all their clients — it's simpler to have one testing protocol, and it demonstrates professionalism.

Chemical Testing Requirements

PWTAG's Code of Practice specifies when and what to test.

Before pool opening and throughout the operating day (public pools):

• Free chlorine
• pH
• Water temperature

For busy public pools, PWTAG recommends testing every 2 hours during operation. For smaller or lower-use pools, less frequent testing may be acceptable — but the "before opening" test is non-negotiable.

At every service visit (minimum for service engineers):

• Free chlorine (target: 0.5–3.0 mg/L; aim for 1.0–2.0 mg/L in practice)
• Combined chlorine (target: ≤1.0 mg/L; calculate from total minus free)
• pH (target: 7.0–7.4)
• Water temperature

Weekly:

• Total alkalinity (target: 80–200 mg/L as CaCO₃)

Monthly:

• Calcium hardness (target: 75–500 mg/L as CaCO₃)
• Microbiological testing (laboratory samples — see below)

For the full parameter table with test methods, see our water testing guide.

Microbiological Testing

Chemical tests tell you the sanitiser is present. Microbiological tests tell you the treatment regime is actually working. PWTAG recommends monthly lab testing for:

Parameter	Target	What It Indicates
Total viable count (TVC) at 37°C	<100 cfu/mL	General bacterial contamination
Coliforms	<10 per 100 mL	Faecal or environmental contamination
E. coli	None detected in 100 mL	Direct faecal contamination
Pseudomonas aeruginosa	<10 per 100 mL	Biofilm presence, filter/pipework issues

Hydrotherapy pools require weekly microbiological testing due to higher risk from immunocompromised users.

Samples must be collected in sterile containers with sodium thiosulphate (to neutralise chlorine and prevent continued disinfection during transport) and delivered to an accredited laboratory within 24 hours, refrigerated. If you're not currently arranging microbiological testing for your commercial clients, it's a service gap worth filling — most operators don't know how to organise it themselves.

What Your Records Must Include

PWTAG's Code of Practice specifies record-keeping requirements. For every pool on a commercial site, records should document:

• Date and time of every test
• Identity of the person who conducted the test
• All parameter results — not just "passed" or "in range", but the actual numeric readings
• Corrective actions — what was dosed, how much, and why
• Equipment details — which photometer or test kit was used, last calibration date
• Microbiological results — filed alongside routine chemical test records
• Incident records — any water quality failures, pool closures, or faecal accidents

PWTAG recommends keeping records for at least five years. This is a practical minimum — some local authorities may expect longer retention for certain types of facilities.

The key point: a record that says "chlorine OK, pH OK" is not compliant. The record must contain the actual reading (e.g., "free chlorine 1.4 mg/L, pH 7.3") and any action taken.

How to Sample Correctly

Sampling technique affects results. PWTAG guidance on sample collection:

• Collect from 300 mm below the surface (not the surface itself, which may be affected by UV degradation)
• Sample away from return jets and dosing points — these give artificially high readings
• Rinse the sample vessel three times with pool water before filling
• Test chemical parameters immediately — chlorine levels change within minutes
• For microbiological samples, use pre-sterilised bottles with sodium thiosulphate

The PWTAG Code of Practice

The full PWTAG Code of Practice is available from PWTAG's website. The definitive technical reference is their book Swimming Pool Water: treatment and quality standards for pools and spas, which the Code is based on.

PWTAG also publishes Technical Notes that update and supplement the Code on specific topics — microbiological testing (TN53), cryptosporidium response, and water treatment system design, among others.

For engineers servicing commercial pools, owning or having access to the PWTAG book is a professional essential. It typically costs around £40 and pays for itself the first time a client asks you to explain a compliance requirement.

Using PWTAG Compliance as a Business Advantage

Many pool operators don't know what PWTAG requires. When you can explain the testing standards, produce compliant records, and arrange microbiological testing, you're offering a service that's measurably better than an engineer who just "checks the chlorine." That's a pricing justification and a client retention tool.

Use our free PWTAG water testing log template to produce structured compliance records from your site visits. PoolRound is building this into a fully automated workflow — log readings on your phone, generate PWTAG-compliant reports automatically. Join the waitlist.

Sources

• PWTAG Code of Practice — Industry code of practice for pool water treatment
• PWTAG Standards — Standards and guidance hub
• PWTAG Technical Note TN53: Microbiological Testing — Microbiological sampling guidance
• PWTAG Swimming Pool Technical Operator (SPTO) — PWTAG operator qualification