PWTAG: A Guide to UK Pool Water Standards

If you work on commercial UK pools or hot tubs, PWTAG sets the rules you're expected to follow. Yet many engineers and operators have only a vague idea of what PWTAG actually is, what it publishes, or how its standards relate to the law.

This guide explains what PWTAG is, what it produces, and what its water testing standards mean for your day-to-day work as a service engineer.

What is PWTAG?

PWTAG stands for the Pool Water Treatment Advisory Group. It was established as an independent entity in December 1984 and has, since then, become the recognised UK authority on pool water quality and treatment.

PWTAG's membership is drawn from statutory, voluntary, and professional organisations with an interest in pool water — including environmental health, leisure operators, chemical suppliers, training bodies, and the swimming pool industry. Because the group is independent, it can give technical advice without commercial influence. In March 2009, PWTAG Ltd was established as a company limited by guarantee to support the organisation's expanding work.

PWTAG's brief covers:

Research into pool water treatment (e.g. cryptosporidium control, filtration)
Standards and guidelines for pool design, treatment, and operation
Product assessment and accreditation (the PoolMark scheme)
Training materials and accreditation of pool operator training providers
Advice to pool managers, local authorities, environmental health teams, and industry

PWTAG was also one of the authors of the World Health Organization's guidelines on safe recreational water environments, which is the international counterpart to UK practice.

What PWTAG Publishes

There are four main documents UK pool service engineers should know about:

1. Swimming Pool Water (the book). PWTAG's definitive technical reference, covering treatment, water chemistry, microbiological standards, plant design, and pool operation. A new edition was published in 2009 and the book has been updated since. Costs around £40 from PWTAG and pays for itself the first time a client asks you to explain a compliance requirement.

2. The Code of Practice. First published in 2012 and based on the book, the Code of Practice is the practical benchmark for pool operation. It also underpins PWTAG's PoolMark certification scheme. This is the document most often referenced in compliance discussions.

3. Technical Notes. Shorter focused documents that update and supplement the Code on specific topics — microbiological testing (TN53), cryptosporidium response, hot tub operation, plant design, and others. Technical Notes are how PWTAG keeps guidance current between editions of the book.

4. PWTAG Standards. A summary of the key target parameters and operational requirements — useful as a quick-reference alongside the Code.

You can find the current list at pwtag.org/standards/ and pwtag.org/technical-notes/.

Is PWTAG Guidance Law?

No — PWTAG guidance is not legislation. PWTAG itself is an independent advisory body, not a regulator.

However, PWTAG guidance is treated as the benchmark of good practice in UK pool operation. Local authorities and the Health and Safety Executive (HSE) reference PWTAG standards when investigating complaints or incidents. Courts have used PWTAG standards as the measure of "reasonable care" when assessing whether a pool operator met their duty under the Health and Safety at Work etc. Act 1974.

In practice, if you're servicing a commercial, shared-use, or holiday-let pool and something goes wrong, the question your client (or their insurer, or a court) will ask is whether the pool was being managed in line with PWTAG guidance. Following PWTAG is what "reasonable care" looks like for pool water.

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: 1.0–3.0 mg/L; 1.0–2.0 mg/L for indoor pools, with 3.0 mg/L the upper limit)
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

PWTAG Training: SPTO and ODS Qualifications

PWTAG also runs the recognised UK qualifications for pool operators. The two main ones are:

Swimming Pool Technical Operator (SPTO) — for staff with day-to-day responsibility for pool water quality and plant operation
On-Site Designated Supervisor (ODS) — for the staff member with overall responsibility for a pool's operational safety

Holding (or your clients' staff holding) an SPTO or ODS qualification is increasingly expected by insurers and local authorities. If you regularly service commercial sites, asking about staff training is part of a proper compliance conversation.

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: Who Are PWTAG? — PWTAG's history, remit, and mission statement
PWTAG Code of Practice — Industry code of practice for pool water treatment
PWTAG Standards — Standards and guidance hub
PWTAG Technical Notes — Supplementary technical guidance
PWTAG Swimming Pool Technical Operator (SPTO) — PWTAG operator qualification