Health risk related to water supply and consumption in a marginalised urban area

Abstract

The main aim of this study was to investigate the microbiological and aesthetical water quality used in large low socio-economic urban settlement. Previous studies in the same area indicated that microbiological quality of municipal supply water was good but, once fetched from municipal supplies, the microbiological water quality of container-stored water deteriorated to become unsafe for human consumption. The previous studies revealed biofilm forming inside container walls, possibly adversely affecting the microbiological quality of the stored water. To confirm this assumption (deterioration associated somehow with formation of biofilm in containers) a simple biofilm assessment method was developed. Epidemiological surveys were conducted simultaneously in the same study area by co-workers studying effects of water quality on human health using diarrhoea as health indicator. From the analyses of data collected, a case-control follow-up study was done of selected households (affect versus not affected by diarrhoea). The quality of water used by the cases and controls was assessed to determine if there were any statistically significant differences in water used by the 2 groups. The effect of distance on the microbiological water quality in containers was investigated as well as the effect of container material of the vessels used by the 2 groups. Heterotrophic bacteria levels in both the supply water and container water were above the negligible risk limits proposed by the South African Water Quality Guidelines (DWAF, 1996) with heterotrophic bacteria numbers in container water higher. Heterotrophic bacteria numbers in container water containing suspended biofilm were significantly higher than in water before suspension. Heterotrophic bacteria levels in water used by both groups were above negligible limits, with the case-group significantly higher than the controls. Turbidity (NTU) in the supply water and container water were below the maximum limits for significant risk proposed by DWAF (1996). NTU in the container water were slightly higher than in municipal supplied water. NTU levels in the water used by cases were slightly higher than that used by control group. Higher total coliforms (TC) levels were observed in stored water than in supply water. TC levels in the container water were above limits for negligible risk. Escherichia coli (E. coli) were intermittently found in supply and container water, indicating occasional risk of exposure for consumers. E. coli numbers in container water were higher than in supply water. E. coli before and after suspending biofilm had similar geometric mean values for cases and controls. Clostridium perfringens (CP) were present in municipal water supplies and container-stored water with both waters having similar mean values. However, the levels did not exceed risk limits. No somatic coliphages could be detected in the containers water and supply water at any stage. Water used by the case and control groups were found to be of equally poor microbiological quality. It was found that water that had to be carried over distances of between 10m and 100m contained more total coliforms than water that was carried over distances of less than 10m and more than a 100m. This was probably due to large open-mouthed containers used, which was conducive to environmental contamination. No statistical significant difference was observed in the microbiological water quality in plastic or metal containers. The microbiological quality of supplied municipal water did not comply with the microbiological limits in terms of DWAF (1996) for heterotrophic bacteria and total coliforms. However, E. coli and CP levels did comply with the limits of DWAF (1993) and Water Quality Criteria (Aucamp and Vivier, 1990).