Sanitary inspection of wells using risk-of-contamination scoring indicates a high predictive ability for bacterial faecal pollution in the peri-urban tropical lowlands of Dar es Salaam , Tanzania

Sanitary inspection of wells was performed according to World Health Organization (WHO) procedures using risk-of-contamination (ROC) scoring in the peri-urban tropical lowlands of Dar es Salaam, Tanzania. The ROC was assessed for its capacity to predict bacterial faecal pollution in the investigated well water. The analysis was based on a selection of wells representing environments with low to high presumptive faecal pollution risk and a multi-parametric data set of bacterial indicators, generating a comprehensive picture of the level and characteristics of faecal pollution (such as vegetative Escherichia coli cells, Clostridium perfringens spores and human-associated sorbitol fermenting Bifidobacteria). ROC scoring demonstrated a remarkable ability to predict bacterial faecal pollution levels in the investigated well water (e.g. 87% of E. coli concentration variations were predicted by ROC scoring). Physicochemical characteristics of the wells were not reflected by the ROC scores. Our results indicate that ROC scoring is a useful tool for supporting health-related well water management in urban and suburban areas of tropical, developing countries. The outcome of this study is discussed in the context of previously published results, and future directions are suggested. doi: 10.2166/wh.2012.117 Douglas Mushi Department of Biological Sciences, Sokoine University, P.O. Box 3038, Morogoro, Tanzania Denis Byamukama Department of Biochemistry, Makerere University, P.O. Box 7062, Kampala, Uganda Alexander K.T. Kirschner Institute for Hygiene and Applied Immunology, Medical University of Vienna, Austria Robert L. Mach K. Brunner Andreas H. Farnleitner (corresponding author) Institute of Chemical Engineering, Research Area Applied Biochemistry and Gene Technology, Research Group Environmental Microbiology and Molecular Ecology, Vienna University of Technology, Gumpendorferstraße 1a, A-1060 Vienna, Austria E-mail: A.FARNLEITNER@aon.at Alexander K.T. Kirschner Andreas H. Farnleitner InterUniversity Cooperation Centre Water and Health www.waterandheatlh.at


INTRODUCTION
Inadequate maintenance of the microbial quality of groundwater in peri-urban areas of developing countries is compounded by many factors, including high-priced microbiological infrastructure and the low level of socioeconomic conditions (Butterfield & Camper ).As a result, peri-urban communities consume water of unknown quality, which may put them at an unacceptable risk of infection by enteric pathogens (Hutin et al. ).This situation calls for simple, feasible and easy-to-perform methods to help peri-urban communities understand, react to and subsequently manage the quality of well water.
Sanitary inspection, which identifies actual and potential sources of contamination of groundwater abstraction points, was proposed by the World Health Organization (WHO ) as part of the comprehensive and complementary risk-based assessment of drinking water quality (WHO ; Luby et al. ).This proposal supports the operation and maintenance of water points by providing clear guidance for remedial action to protect and improve the water supply (Luby et al. ).The WHO () established a format for sanitary inspection forms consisting of a set of questions which have 'yes' or 'no' answers (cf.Supplementary Table S1, available online at http://www.iwaponline.com/jwh/010/117.pdf).The questions are structured such that 'yes' answers indicate that there is a reasonable risk of contamination and 'no' answers indicate that the particular risk appears to be negligible.Each 'yes' answer scores one point and each 'no' answer scores zero points.At the end of the inspection, the points are totalled, yielding a sanitary inspection risk score (in this study, referred to as a risk-ofcontamination, or ROC, score).A higher ROC score rep-

MATERIALS AND METHODS
It is important to note that the study published by Mushi

Risk of contamination scoring
On-site sanitary inspections and well-water sampling from the nine chosen wells were performed from May to July 2005.This period was characterised by wet and dry climatic patterns.ROC scoring was performed according to the questions proposed by the WHO () as given in Table S1 (supplementary material, http://www.iwaponline.com/jwh/010/117.pdf).The ROC scores range from a low risk of contamination (scores ¼ 0-30%), through a medium (40-50%) or high (60-70%) risk of contamination, to a very high risk of contamination (80-100%).The method used to calculate these scores is described briefly above in the Introduction.

Water quality investigations
Water samples were taken at the time of the sanitary inspec-

RESULTS AND DISCUSSION
The surveyed wells showed a distinct pattern of ROC scores ranging from 20 to 100%.Based on the ROC scoring, the surveyed wells (W1-W9) could be placed into four categories, as suggested by the WHO (): low (W1-W3); medium (W4), high (W5 and W6) and very high (W7-W9) risk wells (Table 1).The ROC-based categories correlated remarkably well with the levels of bacterial faecal pollution as determined by the multi-parametric microbial pollution  The high faecal pollution levels in various wells identified by the sanitary survey suggest that the well water is resents a greater risk that drinking water is contaminated by faecal pollution from the area immediately surrounding the well (Lloyd & Batram ; WHO ; Godfrey et al. ; Luby et al. ; Vaccari et al. ; Parker et al. ).Limited data exist on the performance of such sanitary inspection tools (Lloyd & Batram ; Godfrey et al. ; Luby et al. ; Vaccari et al. ; Parker et al. ), especially in most developing and tropical countries like Tanzania.Moreover, the few existing investigations are based on a small set of standard faecal indicator bacteria (SFIB) such as faecal coliforms, Escherichia coli and enterococci and are thus potentially prone to an indication bias or limited to give a more holistic picture of the actual faecal pollution situation (e.g.recent versus past faecal pollution).This is especially significant in tropical environments where SFIB may originate from nonfaecal sources (such as soil) and proliferate in aquatic habitats under favourable conditions, thus resulting in detection at levels that may not reflect the actual extent of faecal contamination (Solo-Gabriele et al. ; Byamukama et al. ; Ishii & Sadowsky ).Consequently, there is a need for investigations concerning the performance of ROC scoring in tropical environments based on robust faecal pollution diagnostics.The aim of this study was to evaluate the predictive capacity of ROC scoring, based on simple-to-perform sanitary inspections according to the WHO guidelines, regarding the extent of bacterial faecal pollution in well water in a peri-urban area of a tropical, developing country.The analysis was based on a selection of wells representing environments ranging from low to high presumptive faecal pollution risk.To integrate the information regarding the extent of bacterial faecal pollution, a multi-parametric data set including SFIB, alternative faecal indicators (i.e.Clostridium perfringens spores and sorbitol-fermenting Bifidobacteria) and physicochemical parameters were investigated.We hypothesised that ROC scoring would accurately predict risk levels for bacterial faecal pollution in Tanzania, a tropical and developing area, thus representing a useful tool for well-water quality management.
et al. in 2010 is based on the same field investigation described in this work.Mushi et al. () focused on the ecology of sorbitol-fermenting Bifidobacteria (SFB) in streams and groundwater in a tropical environment, using lumped data from the collected well water samples.However, the current study focuses on the ROC scoring based on a detailed analysis of the same wells in a variety of locations and over a span of three months.Selection of the wells Wells were selected using weighted random sampling from the peri-urban area of Dar es Salaam, Tanzania (6.2 W S, 39.2 W E). The approach covered well environments ranging from low to high presumptive faecal pollution risk based on the stratified randomisation according to Byamukama et al. ().Wells W1, W2 and W3 are situated in heavily vegetated areas without nearby stagnant water, septic tanks, pit-latrines, human residences or anthropogenic activities.Residents travel approximately 200-300 m from their houses to collect water from these wells.Well W4 is situated approximately 100 m from human residences.Ponding was evident around the well.Neither septic tanks/pit-latrines nor fences were observed within 30 m of the well.Wells W5 and W6 were situated close (approximately 3-5 m) to roads.Septic tanks and pit-latrines were observed at approximately 15 m from the well.Ponding was evident at approximately 10 m from the well, as the drainage channel was faulty.Although wells W1-W6 were well-constructed, no apparent protective measures had been taken against anthropogenic activities.Wells W7, W8 and W9 were chosen as they are situated in a highly populated area with poor sanitary infrastructure.These wells are poorly constructed and poorly protected.The walls of the wells are cracked, with broken platforms that allow growth of algae on the walls and influx of stormwater and runoff.The drainage channels are dirty and broken, allowing ponding.Some of the wells are close to roads and surface runoff, or are within 5 m of poorly constructed septic tanks/latrines situated uphill of the well site.A map of the well locations is given in Mushi et al. ().
tions from the nine wells described by Mushi et al. () using 1 L sterile glass bottles and aseptic technique, according to American Public Health Association (APHA) standard methods (APHA ).Each well was sampled six different times over three consecutive months (from May to July 2005), yielding a total of 54 water samples.Field analysis (dissolved oxygen, temperature, electrical conductivity and salinity), microbiological analysis (presumptive total coliforms, TC; presumptive E. coli; presumptive faecal coliforms, FC; presumptive C. perfringens, CP; and presumptive SFB) and chemical parameters (nitrates plus nitrites, hardness and chlorides) were determined as described in Mushi et al. ().Statistics E. coli concentrations were expressed as logarithmic transformations (log 10 ).Statistical analyses were performed with the Statistical Package for Social Sciences version 11.0 (SPSS Inc., Chicago, IL, USA).A non-parametric Kruskal-Wallis test was used to compare the median number of faecal bacteria in each contamination risk category.A Bonferroni correction was applied in cases where parameters were tested multiple times.The ROC score was calculated as the percentage of total positive answers to the ten questions posed by the checklist.A Spearman rank correlation analysis included the ROC score, potential microbial indicators of faecal pollution and physicochemical water quality parameters.A discriminant analysis of faecal indicator bacteria and ROC data, using Wilks' lambda and a within-group covariance matrix, was performed to cluster wells with the same risk level.Countable microbial colonies were expressed as colony forming units (CFU) per 100 mL.Probability (p) values below 0.05 were considered statistically significant.
occurring SFB) is not unexpected, as all of the considered parameters are by definition associated with faecal contamination.The faecal indicator with the highest association with the ROC score was chosen to further investigate the predictive capacity of ROC scoring.Regression analysis indicated that the ROC score was able to successfully predict up to 87.4% of the E. coli concentrations among the investigated wells (Figure 1).The results from a discriminant analysis of the multiparametric bacterial pollution parameters and the ROC data, using Wilks' lambda and the within-group covariance matrix, closely mirrored the four clusters classified by ROC scoring (Figure 2).The first and second discriminants accounted for 96% of the observed variation, suggesting that the selected wells exhibit distinct levels of contamination and that the wells with the same level of contamination are tightly clustered by ROC scores and the bacterial faecal pollution data.In contrast, this tight grouping was not observed when ROC scores and physicochemical parameters were subjected to discriminant analysis using the same algorithms because the first and the second discriminants accounted for <10% of the variation (see also Table S2 supplemental material online at http://www.iwaponline.com/jwh/010/117.pdf).This result is most likely due to comparable hydrogeochemical conditions among the investigated well catchments (p > 0.05, n ¼ 45-54, Kruskal-Wallis test).These results provide evidence that bacterial faecal pollution is closely linked to the sanitary hazards identified by the wells' ROC scores (Figure 1).Thus, the combination of sanitary inspection and analysis of microbiological water quality may also be useful for identifying the most important causes of and control measures for well contamination, which is important to support effective and rational decision-making.For instance, it will be important to know whether on-site (in association with the construction and maintenance of the location and its immediate inner protection zone) or off-site (in association with the catchment protection of the well) sanitation could be associated with the contamination of drinking water, as the remedial actions required to address either source of contamination will be very different.Such analysis may also identify other factors associated with contamination, such as heavy rainfall.It may be useful to complement such combined analysis with viral faecal indicators (e.g.somatic coliphages) to avoid underestimating viral mobility by focusing solely on bacterial parameters in porous groundwater resources.However, the results of the current study most likely relate equally to bacteriological, viral and protozoan faecal hazards, as microbial faecal contamination directly at the site of the well is considered to be the primary source of contamination (such as due to cracks in the well walls).

Table 1 |
ROC scores (%), microbial indicators of faecal pollution (CFU/100 mL) and physicochemical parameters of water quality in peri-urban wells sampled during the study period p > 0.05, n ¼ 18; TableS2).SFB could only be detected in water samples from very high risk wells (W7-W9), demonstrating that these wells were contaminated very recently with human faecal pollution(Mushi et al. ).It should be noted that the tight correlation between all of the investigated faecal indicators (except for the less abundantly