Study Area Kushtia district is located in the Khulna administrative division of the western part of Bangladesh. It is bordered by the Padma River to the north, Jhenaidah districts to the south, Rajbari district to the east, Meherpur, Chuadanga districts and Nadia & Murshidabad districts of West Bengal (Indian State) to the west.
Sampling The drinking water samples were collected for Physico-chemical analyses in prewashed (with detergent, distilled water, diluted HNO3 and de-ionized water, respectively) high-density polyethylene (HDPE) bottles (2.0 L) from randomly selected thirty-two different sources in the region of Kushtia district. All samples were kept in the refrigerator at 4 °C to complete the experiment. On-site measurement of water samples was performed for electrical conductivity (EC), pH, and total dissolved solids (TDS). The water sample was collected in another 500 mL sterilized borosilicate glass bottles for bacteriological analyses (Fecal Coliform and Total Coliform) and carried out within 4 h after sampling. The sampling points and locations were confirmed by GPS meter (MacGellan Triton, USA).
Reagents Analytical grade chemical reagents were used for the preparation of all solutions. Freshly prepared deionized distilled water was used in all experiments. Arsenic (As), Manganese (Mn), and Iron (Fe) standard solutions were from Fluka-Analytical, Switzerland. Twenty percent potassium iodide (Sigma-Aldrich, USA) solution was used to reduce As (V) to As (III). Arsenic trihydride (AsH3) generation was performed with 5 M HCl (Sigma-Aldrich, USA), 0.6% sodium borohydride solution (Sigma-Aldrich, USA). MFC and mENDO agar were from Himedia, India used for bacteriological tests.
Physico-Chemical Analyses The Physico-chemical properties of the collected water samples were measured in terms of pH, EC, Total Hardness, As, Fe, and Mn. pH and EC of the water sample were measured on-site using a multimeter (Model HQ 40d, HACH, USA). Meter was calibrated by using two buffer solutions of pH 4.01 and pH 7.00 before analysis. Meter was frequently verified using standard buffer solution after the pH measurement of each five samples. Meter was also calibrated by using standard 1000 µS/cm NaCl solution and verified after five measurements for EC determinations. Hardness was determined by the standard EDTA (0.01M) solution using the complexometric titration method. Trichrome Black T is used as an indicator. As, Mn, and Fe contents were analyzed by atomic absorption spectrophotometer (Varian AA220, Australia). The amount of total arsenic was determined by the hydride vapor generation process at 193.7 nm wavelength using argon gas as a carrier. Apart from arsenic the amount of iron and manganese were determined by the atomization process at the wavelength of 248.3 nm and 279.5 nm, respectively.
Bacteriological Analyses Membrane filtration method was used for the presence of fecal coliforms and total coliforms. Aliquots of 100 mL from each sample was filtered using 0.45 µm paper filters. The filters were placed on mFC and mENDO agar and then incubated aerobically at 44.5 °C and 37.5 °C respectively for 21±3 hrs. Blue and metallic sheen (Golden Red) colonies on MFC and mENDO agar plates were purified and used for bacteria identification tests. Further confirmatory tests were also performed for purposes of identification (ISO, 1986).
Data Analysis Data for Physico-chemical and bacteriological contaminants in drinking water samples were recorded and analyzed for pH, EC, Hardness, As, Fe, Mn, FC and TC. Mean and standard deviations were calculated. Errors were calculated to ±5% during analysis. Water quality results were compared with the Department of Environment (ECR’97), Bangladesh and the WHO drinking water quality standards.