Water quality problems associated with intermittent water supply

Abstract

A controlled study was conducted in Lebanon over a period of 12 months to determine bacterial regrowth in a small network supplying the Beirut suburb of Naccache that had a population of about 3,000. The residential area, which is fed by gravity, is supplied twice a week with chlorinated water from two artesian wells of a confined aquifer. A significant correlation was detected between the turbidity and the levels of heterotrophic plate count bacteria (HPC) in the samples from the distribution network as well as from the artesian wells. However, a negative significant correlation was found between the temperature and the HPC count in the samples collected from the source. A statistically significant increase in counts, possibly due to regrowth, was repeatedly established between two sampling points lying on a straight distribution line but 1 km apart. Faecal coliforms were detected in the source water but none in the network except during a pipe breakage incident with confirmed Escherichia coli reaching 40 CFU/100 mL. However, coliforms such as Citrobacter freundii, Enterobacter agglomerans, E. cloacae and E. skazakii were repeatedly isolated from the network, mainly due to inadequate chlorination. A second controlled study was conducted to determine the effect of storage on the microbial quality of household storage tanks (500 L), which were of two main types - galvanized cast iron and black polyethylene. The mean bacterial count increased significantly after 7 d storage in both tank types. A significant difference was found in the mean HPC/mL between the winter and the summer. Highest counts were found April-June although the maximum temperature was reported later in the summer. A positive correlation was established between the HPC/mL and pH, temperature and storage time.