The microbiological quality of groundwater-derived drinking water after long storage in household containers in a rural community of South Africa

Abstract

To investigate the effect of long storage and household containers on the microbiological quality of water in a rural community, borehole water from the reservoir and seven standpipes was used. Borehole water was stored for a period of 72 h in household containers (polyethylene-PE and galvanised steel-GS), which are commonly used by the rural community of Mgquba village. Heterotrophic plate count (HPC) and faecal coliform bacteria were used as the main parameters. Standard spread plate procedure and membrane filtration method were used to enumerate HPC and faecal coliform bacteria respectively. The results of this study revealed three factors that affected the microbiological quality of drinking groundwater used by the rural community of Mgquba village: the intake water, the duration of storage and the household container. The initial levels of faecal coliform (range of faecal coliforms: 0.1–2 cfu · 100 ml −1 in the reservoir water, 0–57 cfu · 100 ml −1 in the standpipe water) and HPC bacteria (average counts: 5 log cfu · ml −1 in the reservoir water, 7 log cfu · ml −1 in the standpipe water) in both reservoir and standpipe waters far exceeded the limit allowed by the South African Water Quality Guidelines for Domestic Use (no risk target water quality range: 0 count · 100 ml −1 for faecal coliforms, 0–100 counts · ml −1 for HPC bacteria). The persistence of faecal coliforms in polyethylene-stored water was observed after 72 h of storage while their complete elimination in the galvanized steel-stored water occurred after 48 h of storage. Escherichia coli was the most dominant faecal coliform found in the initial and stored waters. Although the yield of HPC bacteria increased in water samples during storage in both polyethylene and galvanised steel containers, the microbiological quality of drinking groundwater deteriorated consistently with the length of the storage. Water stored for 72 h displayed a higher yield of HPC (average counts: 7 log–8 log cfu · ml −1 in PE-stored water, 6 log–8 log cfu · ml −1 in GS-stored water) than the water stored for 48 h or 24 h (average counts: 5 log–8 log cfu · ml −1 in PE-stored water, 5 log–7 log cfu · ml −1 in GS-stored water). Statistical analysis indicated a significantly higher number of HPC bacteria in the water stored in polyethylene than in the water stored in galvanised steel ( P =0.02). Significant differences in HPC bacteria were also noted within household container-stored water from standpipes ( P =0.0001 for PE, P =0.0002 for GS).