Abstract
M. Tech.
The study assessed the risk of infection introduced by containers in which households collect water
from different sources. The study area was in rural villages in the Vhembe region of the Limpopo
Province. Each village had its own unique water sources consisting mainly of untreated ground
waters and untreated surface waters. Randomly selected household members use their containers
to collect water from these different sources. Two of the three villages received new small water
supply systems within the study period, proving the villagers with water of good health-related
microbial quality. The remaining village continued to use contaminated water from their untreated
surface water sources. The water supply intervention in two of the three villages provided the
opportunity to assess the impact these interventions would have on the risk of infection i.e. whether
the risk could be reduced for the villagers no having access to good quality water.
A customized quantitative microbial risk assessment was done based on the health-related quality of
the water that people ingested before and after the intervention. This assessment was based on
exposure of, consequence to and impact on an individual water consumer. Exposure included
variables such as daily quantities of unheated drinking water consumed per individual (in litres)
available at the point of use (in the dwelling) for ingestion, numbers of diarrhoeagenic E. coli (Dec)
per litre in water sampled from containers derived from water samples positive for indicator E. coli
and daily doses of DEc per litre ingested by an individual in the target population. Consequence was
assessed by calculating the probability of infection per day from diarrhoeagenic E. coli for an
individual and from there the annual infection per individual. The impact of the small water supply
system was determined by assessing changes in annual individual risk of infection from before to
after the interventions per village.
In terms of daily water volumes consumed per individual, there were no significant differences in
consumption amongst the three villages. At 1.26 ℓcd (at the upper limit of the 95% confidence
interval) the consumption was slightly higher than the one litre suggested by WHO 2003. The
container water collected from sources before the intervention in the two villages was significantly
more contaminated by indicator E. coli (iEc) and diarrhoeagenic E. coli (DEc) than their container
waters after the intervention.
In terms of impact, the risk of infections was substantially reduced by the interventions. For Village 1
the risk of infection was reduced from 646 infections to 135 infections per 10,000 of the population.
If these are converted to 10% as disease manifesting, then there could have been 65 cases of enteric
disease attributable to water before the intervention, which was then reduced to 14 cases after the
intervention. For Village 2 the population risk was reduced from 110 to 67 cases after the
intervention. For Village 3 the population risk remained at 2,778 infections or 278 cases of enteric
waterborne disease because of their continued use of untreated water.
The study findings indicated that for Village 1, the population risk of infection would be 135
infections per 10,000, for Village 2 it would be 167 and for Village 3 - 234. If the hypothetical
conversion rate of one case of enteric waterborne disease for every 10 infections of Howard et al.
(2006) is used, then this would mean 14 cases of disease per 10,000 for the population for Village 1,
17 cases for Village 2 and 24 cases for Village 3. Relating this to the WHO (2003) suggestion of one
case per 1,000 as an acceptable, it would mean 1.3 cases for Village 1, 1.7 for Village 2 and 2.4 for
Village 3. For Village 1 the risk of contracting waterborne enteric disease was close to acceptable,
but not at all acceptable for the other two villages, even for Village group 2 after the intervention.
The water system in Village 2 failed often during the study which was probably the cause of the
persistently higher risk of disease. It can be concluded that providing a well maintained small water
supply system reduced the risk to and maintained it at an acceptable level.
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