Hydrological controls on the dynamics of E.coli populations in the Romwe catchment, southern Zimbabwe.
A case study of the seasonal variations in indicator bacteria populations
found in water supply wells in a small southern African village has
yielded some disturbing findings. This village is typical of the region but
has also benefited from the installation of a an experimental, higher-
yielding type of wells, a 'collector' or Rannay-type well. In addition to
improved yields, it had been assumed that these types of wells would also
yield better quality water because of their superior construction. A two-
year monitoring programme was carried out to try and understand the
seasonal fluctuations in bacteriological quality terms of the hydrological
controls. The study has confirmed that water quality (as determined by
E.coli population density) in traditional, hand dug well is very variable.
Bacterial population density fluctuates throughout the year but rarely
drops to zero. This is also true for the collector well, demonstrating that
even screened boreholes are pulling water from throughout the regolith,
where soil- and ground-water fluxes ensure thorough mixing, and not
preferentially from the fissured hardrock as usually supposed.
Descriptions of the field techniques employed and resulting data on
microbiological E.coli populations, selected hydrochemical determinands
and basic hydrological parameters are presented. Analysis and
interpretation of the data, together with hypotheses to account for the
variability, form a substantial part of the thesis. The implications of the
findings on health and general socio-economic development issues,
including long-term water supply in similar rural areas, are discussed.