The re-use of treated domestic wastewater necessitates a rigorous control and rapid monitoring of the hygienic quality of the reclaimed water. For this purpose, a new pH-based biosensor was developed. The essence of the methodology of the sensor is the monitoring of the acidification due to bacterial metabolism of added glucose. To improve the sensitivity, the alkalinity of the water sample is reduced prior to monitoring the acidification. This is done by stripping CO2 at a neutral or acidic pH value. The hygienic aspect of the sensor lies in the applied temperature (37 degreesC) and the use of N-2 as decarbonizing gas, thus creating conditions favorable for enteric bacteria. The developed sensor could be used onsite at an advanced stage of treatment, as an endpoint or intake quality control device. For both applications. a useful correlation was obtained between log total plate count and lag time or acidification rate, respectively. Absolute detection limits lay in the ranges of either 10(3) colony-forming units (CFU)/ml in 6 h (endpoint quality control), or less than 10(5) CFU/ml in 1 h (intake quality control).