New guidelines for the microbiological testing of swimming pool water have been issued by the industry's independent watchdog. The Pool Water Treatment Advisory Group (PWTAG), publisher of the authoritative book, Swimming Pool Water treatment and standards, is recommending one extra routine test and new procedures for acting on failures - but no changes to the basic monitoring.

The new guidelines are incorporated in a BSI Code of practice, PAS39:2003 Management of public swimming pools - Water treatment systems, water treatment plant and heating and ventilation systems, which will be published (with a separate press release) in early December. The code of practice is based on Swimming Pool Water - where the relevant chapter will be updated in the new edition to be published in 2004/05.

Meanwhile, we include an EXTRACT from BSI Code of Practice PAS39:2003 for your guidance.

PWTAG chair, Ralph Riley, is confident that the new guidelines will help the industry. 'There's hardly ever been any doubt about what to aim for when testing for bugs. The doubts arise when it comes to knowing what to do when you get a bad result. Do you cross your fingers and hope it's OK next time? Do you shut the pool and get in enironmental health? The answer is neither - and for the first time we have guidelines that make this clear, and spell out a rational plan of campaign'.

Changes - and what hasn't changed
How testing is done, including how frequently, has not changed from the guidelines in Swimming Pool Water. Nor has the time set for incubating water samples for colony counts. Although drinking water samples are now incubated for 48 hours, pool water samples should still be incubated for 24 hours.

The limits for satisfactory levels of colony counts (up to 10cfu per ml), coliforms (absent in 100ml) and E coli (absent in 100ml) are also unchanged.

For the first time, routine testing for Pseudomonas aeruginosa is specified. (Previously testing was recommended only if there were operational or other health problems, or routinely for spas.) The limit now is 10 per 100ml.

The main changes lie in what operators should do faced with unsatisfactory bacterial results and are outlined below....

• If a result is unsatisfactory, the test should be repeated.
• If the second result is also unsatisfactory, the pool's management and operation should be investigated and the test repeated.
• If the third result is still unsatisfactory, immediate remedial action is required, which may mean closing the pool.
• The pool should be closed if there is chemical or physical evidence of unsatisfactory disinfection.
• The pool should be closed if microbiological testing discloses one of two measures of gross contamination:
• E coli over 10 per 100ml PLUS either colony count over 10cfu per ml or P aeruginosa over 10 per 100ml (or, of course, both)
• P aeruginosa over 50 per 100ml and colony count over 100 per ml.