The quality of drinking water supplies in North-Western Greece: a three-year follow-up

Abstract

The study was undertaken to assess the microbiological and physicochemical quality of potable water of Arta, Preveza and Lefkada prefectures in North-Western Greece, during a 36-month survey (1996–1999). Drinking-water samples were collected from twelve points along the distribution networks located at the three cities of Arta, Preveza and Lefkada. The drinking-water quality standards were analyzed with respect to the presence of total coliforms (TC), fecal (thermotolerant) coliforms (FC) and fecal streptococci (FS). Some physicochemical parameters such as temperature, pH and total dissolved solids (TDS) were also determined. Standard techniques for water sample collection and analysis set by the American Public Health Association were used. Microbiological analyses indicate that of the 456 samples analyzed along the distribution network from the springs to the consumer potable tap, the individual failure rates were 35.1, 27.4 and 12.3% for TC, FC and FS, respectively. The combined failure rate according to the limit set by the 80/778 directive of the European Union was 37.9% for the analyzed samples. Failure rates on microbiological indicators displayed a seasonal trend being greater during the autumn–winter period. Although this observation is likely due to a combination of local and regional scale factors, a part of the variability in the failure rate was explained by a significant positive relationship with the rainfall amount. The results showed that there are considerable variations among the examined samples with respect to their physicochemical properties, which lie below the maximum permissible levels of the European drinking water standards. A higher failure rate for the samples collected directly from the springs compared with those taken from the potable tap suggests that the groundwater itself contributes much of the microbiological contamination and physicochemical alterations rather than the storage or a supply line contamination mechanism.