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).