Bacteriological assessment of dug well water in rural areas of Bangladesh


 This study assessed the bacteriological quality of dug well waters from Jashore district – an arsenic affected area of Bangladesh. A total of 58 dug wells (42 installed by a government organization (GO) and 16 installed by a non-government organization (NGO)) were sampled in the dry and wet seasons. The samples were evaluated for total coliform (TC), faecal coliform (FC) and Escherichia coli (E. coli). Sanitary inspections of the surroundings of the GO-installed dug wells identified the sources of faecal contamination. Both the GO-installed and NGO-installed dug wells had bacterial contamination. The median concentrations of E. coli among the GO-installed and NGO-installed dug wells were, respectively, 41 and 21 cfu/100 ml in the wet season, and respectively 2 and <1 cfu/100 ml in the dry season. In the wet season, 24 and 31%, respectively, of the GO-installed and NGO-installed dug wells were in the high-risk category. All of the dug wells had higher disease burden in the wet season compared to the dry season. The ﬁndings suggest that drinking water from the dug wells is likely to pose health risks to the rural communities.

constructing a well of large diameter, typically lined by concrete rings and enclosed by a concrete slab or metal sheet with ventilation (Howard et al. ; Bain et al. ). In the case of a protective dug well, the well-lining or casing is raised above the ground level and provided with a platform that can draw away spilled water to avoid contamination of surface runoff. This also includes an enclosure of a concrete slab or metal sheet with ventilation to protect the water from bird droppings and animals. Generally, a hand pump is connected to a protective dug well for withdrawing water.
A dug well is typically installed at a shallow depth (1-20 m) which is above the arsenic-contaminated aquifer. there is little information on the product water quality of GO-installed and NGO-installed dug wells located in the arsenic affected rural areas of Bangladesh. The present study was conducted to evaluate the bacterial quality of product water from existing dug wells and to determine potential human health risks due to the consumption of dug well water. It is expected that the outcomes of this study will be useful to develop effective strategies to improve the water quality of dug wells installed in the rural areas of Bangladesh.

METHODOLOGY Study area and dug well
The present study was conducted in Chowgacha sub-district under Jashore district in Bangladesh. Chowgacha sub-district is located within latitudes 23 10 0 N to 23 22 0 N and longitudes 88 54 0 E to 89 08 0 E, covering an area of 269.31 km 2 . The location of selected unions under Chowgacha sub-district is shown in Figure 1. To select the dug wells, we first spoke with relevant officials from GO and NGOs to obtain an overview of the distribution of dug wells in Jashore district. According to the DPHE and NGO officials, most of the dug wells are present in Chowgacha sub-district. We considered seven out of 11 unions of the sub-district for water sampling because the majority of the dug wells were installed in those seven unions (Singhajhuli, Pashapole, Phulsara, Arardha, Narayanpur, Dhuliani and Swarupdaha).
The selected unions have a total population of 231,370.
There are differences in the installation and maintenance of the dug wells installed by the GO and NGO.
According to DPHE and NGO officials, the average depth of GO-installed and NGO-installed dug wells are 20-35 ft and 30-45 ft, respectively. In both cases, a concrete ring is used and the well is lined (cased) with sand to prevent collapse. The top of GO-installed dug wells are generally sealed with a concrete slab and water is withdrawn by a hand pump. NGO-installed dug wells typically have a curb about 1 foot above the ground and another 2/3 feet surrounded by a net, along with the top of the well being covered by a metal sheet with ventilation. NGO-installed dug wells also include a slow sand filter (SSF) to filter the dug well water and a caretaker regularly adds disinfectant (bleaching powder) in the well water by a dropout system.
The GO-installed dug wells have a sealed top (Figure 2), and eventually no maintenance is carried out.

Water sampling
Water samples were collected only from the active dug wells from the selected seven unions of Chowgacha sub-district.
Dug wells installed by the NGO include SSF to treat the water before consumption. In this way, the water from a dug well first goes into a SSF when the water is pumped manually. After filtration, the water is collected from the outlet tap of the SSF. As the GO-installed dug wells do not have any filtration or treatment system included, the product water is collected from the hand pump that is connected with the dug well. Therefore, the samples were collected from hand pumps of the GO-installed dug wells and from the outlet of the SSF of NGO-installed dug wells. Since the dug wells are enclosed by a concrete slab or metal sheet, it was not possible to collect water directly from the dug well. Moreover, the NGO-installed dug well has a hand pump directly connected with the inlet of the SSF thereby stopping the collection of water from the hand pump. As a result, it was not possible to collect water before and after filtration to compare the efficiency of the SSF. Consequently, only product water from the NGOinstalled dug wells was collected. Photographs of typical GO and NGO dug wells are shown in Figure 2. Sterilized nalgene plastic bottles were used to collect water samples.
The sampling procedure described by APHA () was strictly followed to avoid any contamination during the collection and storage of samples. The outlet of the water source was disinfected before taking the sample in disinfected bottles collected from the laboratory. The disinfection procedure included wiping the outlet using clean tissue paper, flushing the water for 1-2 minutes, heating the outlet with an alcohol burner and flushing again for  were collected from all the NGO-installed dug wells available in the Chowgacha sub-district. However, three of the GO-installed dug wells were located in very remote areas with inaccessible road conditions. The reason for not collecting water samples from these dug wells was the transportation of water samples to our laboratory maintaining the time-bound to perform microbiological analysis.

Detection of indicator bacteria
Bacteriological analysis was carried out by the membrane filtration (MF) method. Standard procedure (APHA ) was followed to conduct the analysis. Several dilutions of samples were considered. We considered triplicate plates for each dilution to determine the number of bacteria. Filtration devices were treated by using a burner to ensure proper sterilization and to prevent cross-contamination among samples. To determine the concentration of total coliform (TC), faecal coliform (FC) and Escherichia coli (E. coli), water samples were filtered through different 0.45 μm pore-size membrane filters (Millipore Corp., Bedford, MA, USA), which were then placed on m-Endo, mFC and mTEC agar plates, respectively. The m-Endo and mFC plates were incubated at 35 ± 0.5 C for 24 h and 44 C for 18 to 24 h to determine the TC and FC, respectively. Characteristic pink and blue colonies were noted as TC and FC, respectively. To determine the concentration of E. coli, the mTEC agar plates were incubated at 35 ± 0.5 C for 2 h followed by further incubation at 44.5 ± 0.2 C for 22-24 h.
Then, the filters were transferred to a pad saturated with urea substrate for 15-20 min. After incubation on the urea substrate at room temperature, yellow, yellow-green or yellow-brown colonies were counted as E. coli. The bacterial counts were expressed as colony forming units (cfu) per 100 ml.

Health risk assessment
Disease risk of drinking the dug well water was determined using a quantitative health risk assessment (QHRA) model (Islam et al. ).

Indicator bacterial contamination
The mean, median, minimum and maximum concentrations of TC, FC and E. coli of GO-installed and NGO-installed dug wells product water are presented in Table 1 according to the seasons. The distribution of the concentrations of E.
coli is shown in Figure 3.
The summary of the findings of Table 1  • The minimum concentrations of E. coli and FC were less than 1 cfu/100 ml for both GO-installed and NGOinstalled dug wells' product water in both seasons. Concentrations of TC were higher in all the dug wells' product water during both seasons; however, the greatest median concentration of TC was observed among the GO-installed dug wells product water.

Risk category
Based on the concentration of E. coli, the product water from GO-installed and NGO-installed dug wells was

Health risk assessment
The lower (5th percentile), median and upper (95th percentile) disease burden estimates for GO-installed and NGO-installed dug wells product water according to the seasons are presented in Figure 5. The median disease burden estimates indicate that the disease burden for drinking water from both GO-installed and NGOinstalled wells was higher compared to the WHO recommended reference level of disease burden (1 × 10 À3 DALYs/1,000 person-yr) during the wet season.

Effects of sanitary risk factors
Results of the health risk assessment indicate microbial risk of drinking water from both GO-installed and NGOinstalled dug wells, and the risk was higher in the wet season. We used the data from the sanitary inspection of GO dug wells to identify the sources of microbial contamination. The relevance between individual risk factors and the presence of E. coli is indicated by the odds ratio (OR) ( Table 2). An OR greater than 1 indicates that the corresponding factor might influence the E. coli concentration. We considered E. coli <1 cfu/100 ml as the coli contamination of the GO-installed dug wells was relatively higher compared to those installed by NGO.
However, mean E. coli contamination of the NGO-installed dug wells was higher compared to GO-installed dug wells in the dry season, which indicates very high E. coli contamination in some NGO-installed dug wells. Although NGO dug wells had caretakers, in most of the cases after one year of the construction activity, caretakers were not visible due to the end of the funding period of NGO. All the dug wells were more than one year old and during field visit and sampling, we did not find any activity of caretakers. NGO-installed dug wells include a SSF for treatment of the water before collection. However, the performance of the SSF depends on its regular maintenance. A previous study conducted in southwest coastal Bangladesh also found poor operation and maintenance of pond-sand filters

CONCLUSIONS
This study examined the bacterial contamination of product water of dug wells in an arsenic affected area of Bangladesh.
Water of dug wells installed by both GO and NGO had a should not be allowed within a minimum safe distance of a dug well. A better assessment considering a larger sample size and covering the seasonal variation is required to achieve a more representative insight of the sources of faecal contamination.