The efficiency of pigment extraction forms the crux of the spectrophotometric analysis of chlorophyll a. The alcoholic solvents, methanol and ethanol, proved to be superior to acetone and acetone with DMSO. Homogenisation and sonication did not improve the extraction in the alcoholic solvents. Boiling at 100 O C had an adverse effect whereas complete extraction of the pigments was obtained at the solvents boiling point and allowing the samples to stand for 24 h in the dark.

Legionella pneumophila is an opportunistic pathogen of major concern. The current large volume quantitative method employs membrane filtration (MF) and selective culture on GVPC agar followed by confirmation of isolates by serology (ISO 11731-2) We present here the results of a multi-laboratory evaluation of a most probable number (MPN) in-situ confirmed method (Legiolert™/Quanti-Tray®). The results indicate that Legiolert/Quanti-Tray yielded on average higher counts of L. pneumophila than ISO 11731-2. This development significantly improves and simplifies the enumeration of L. pneumophila from potable water samples.

Two media (mCP medium and Tryptose Sulphite Cycloserine (TSC) agar) were evaluated for recovery of Clostridium perfringens in environmental and part‐treated drinking water. For laboratory strains of Clostridium, mCP was more selective and specific for Cl. perfringens than TSC, but was markedly less efficient for the enumeration of both vegetative cells and spores. For samples of river water and part‐treated drinking water, TSC recovered significantly greater numbers of Cl. perfringens than mCP. In contrast to previous reports, there was a significant number of false presumptive positive and negative isolates on mCP. TSC is a more suitable medium for the routine monitoring of water supplies for the presence of Cl. perfringens.

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A medium for the single membrane enumeration of Escherichia coli and coliforms from potable water was developed by the modification of the standard UK membrane filtration medium. The medium, membrane‐Lactose Glucuronide Agar (m‐LGA), employs a chromogenic substrate for the detection of β‐glucuronidase activity and sodium pyruvate to enhance recovery of chlorine‐stressed coliforms. Escherichia coli identification was significantly improved on m‐LGA with 98.6% of presumptive isolates confirming. Recovery of coliforms from drinking water samples was also significantly improved.