Assessment of microbiological and physico-chemical characterıstics of water samples in households of Bangalore city, Karnataka, India

Access to safe drinking water is one of the basic human rights and is essential to human health (Hall et al. 2013). The quality of drinking water is an essential factor for better human health (Francis et al. 2015). An adequate supply of safe drinking water is one of the most challenging tasks in many developing countries (Ouf et al. 2018). Many people must confront every day the situation of an inadequate supply of water and the very serious consequences (Cosgrove & Loucks 2015).

According to the estimation of the UN (2018), more than 55% of the population is living in an urban area. With the increasing urban population and expansion of urban areas, many city managers are facing the problem of providing an adequate quantity and quality of water (McDonald et al. 2011). Proper sewerage systems also remain challenging tasks for many in urban areas (Wankhade 2015). Consequently, this situation could be a potential threat to the health of citizens. This problem is more serious in India where the rate of urban growth is higher (George 2015).

The rapid growth of the urban population has resulted in increases in the need for basic services and the access to appropriate water supply and sanitation (Satterthwaite et al. 2010). The rapid growth of urban areas has further affected water quality due to the increase of the urban population, over-exploitation of resourses and improper waste disposal practices (McGrane 2016).

Many researchers (Edokpayi et al. 2018; Irda Sari et al. 2018) from different parts of the world have reported the status of drinking water quality in urban areas. The status of water supply and sanitation services in urban areas of India is generally poor and with a limited continuity of water supply (George et al. 2015). In India, no major city is known to have a continuous water supply and it is only available for a few hours per day (McKenzie & Ray 2009). In Bangalore city, the incidence of waterborne infections is consistently high due to a limited supply of drinking water (Sheeba et al. 2017). Many studies have been reported on the physico-chemical quality of drinking water in Bangalore but the hazard identification and health risk-associated assessments have not yet been reported.

This study was based on two aspects of water quality: one is the microbial contamination and the other is focused on physico-chemical parameters. The microbial contamination is mainly due to waterborne pathogens, especially from the members of Enterobacteriaceae. Generally, most of the microbial pathogens are transmitted via contaminated food, but waterborne transmission has been well documented for recreational and contaminated drinking water (Ashbolt 2015). Contaminated drinking water serves as an important vehicle for transmitting both chemical and microbial agents to cause diseases in humans (Hurst 2018). Increasing incidents of waterborne diseases via contaminated drinking water have become a public health problem in both developed and developing countries (Pandey et al. 2014).

The main objective of this research is to assess the microbial health risk generated in the households of Bangalore city and to determine the physico-chemical and microbiological quality of drinking water supply for the end-user. In view of this, an attempt was made to carry out microbiological hazard identification from the households of Bangalore city, Karnataka, India.

This study was carried out in and around Bangalore, Karnataka, India, located at 13.0320°N, 77.6360°E. The city population mainly depends on bore well and Cauvery water sources for drinking purpose.

A total of 20 sampling points were randomly selected and water samples were collected from households of Bangalore, Karnataka, India. The samples were designated as SSW-1, SSW-3, SSW-5, SSW-7 to SSW-11, SSW-14, SSW-15, SSW-17, SSW-19 to SSW-20 and the samples were collected from surface water source (Cauvery water). The samples SGW-2, SGW-4, SGW-6, SGW-12, SGW-13, SGW-16 and SGW-18 were collected from groundwater sources (Table 1).

A survey was conducted during the study period to determine the type of water consumption (Cauvery water, bore well and bottled water). The samples were collected in pre-cleaned, sterilized polyethene bottles. They were analysed by following microbiological and physico-chemical parameters. Microbiological parameters were examined within 2 hours of sample collection. All the measurements were done in triplicate and values were expressed as mean ± standard deviation.

The water samples were analysed for the microbiological parameters heterotrophic plate count (HPC), total coliform count (TCC), faecal coliform count (FCC) and Escherichia coli using standard methods. The total coliform count was determined by most probable number (MPN) technique using a set of three tubes inoculated with 10 mL of lactose broth of different strengths with samples of 10 mL, 1 mL and 0.1 mL. The faecal coliform and E. coli were detected by subculture of all presumptive positive tubes of the coliform test at the end of 48 hours in BGLB medium and incubation at 44.5 °C for 24 hours in a water bath. Bacterial pathogens related to gastroenteritis isolated on respective media were identified on the basis of their morphological and biochemical properties following Bergey's Manual of Determinative Bacteriology (Holt 1994). Biochemical tests such as indole, MR-VP and urease were performed for phenotypic identification of enteric isolates.

On-site analyses of pH, conductivity, turbidity and temperature were carried out at the site of sample collection following the standard protocols and methods of the American Public Health Agency. Total hardness was measured according to the standard methods (APHA 2005). Winkler's method (APHA 2005) was used for determination of the dissolved oxygen (DO) using azide modification. All the measurements were done in triplicate and values were expressed as mean ± standard deviation.

The microbiological and physico-chemical parameters of water samples were compared to the water quality guidelines of CPHEEO (2009), BIS (2012) and WHO (2017). Microbiological and physico-chemical characteristics of water samples are presented in Table 2.

The results of the study show that most of the household water samples were contaminated with coliform bacteria (Figure 1). The SSW-1 sample showed the highest count (1,600 MPN/100 mL) among other samples. Sampling stations SSW-5, SSW-8, SSW-9, SSW-10, SGW-12, SSW-19 and SSW-20 showed a similar pattern of TCC (1,100 MPN/100 mL). The water samples SGW-2, SGW-6, SSW-7, SGW-13 and SGW-16 have a similar pattern of TC count (210–240 MPN/100 mL). The sampling points SSW-4 and SGW-15 are less contaminated in terms of TC count (13 MPN/100 mL). The water samples SSW-3, SSW-11, SSW-17 and SGW-18 showed TC count within the permissible ranges of WHO (2017) and BIS (2012).

The faecal coliform count (FCC) was higher for SSW-1, SSW-5, SSW-8, SSW-10, SGW-12, SSW-19 and SSW-20 (11–24 MPN/100 mL). The water samples SGW-2, SSW-7, SSW-9, SGW-13, SSW-14 and SGW-16 were moderately contaminated with faecal coliforms. The water samples SSW-3, SSW-4, SSW-11, SSW-15, SSW-17 and SGW-18 showed FC count within the permissible range of WHO (2017) and BIS (2012).

The bacteria belonging to the family Enterobacteriaceae showed a greater percentage of bacterial population isolated from the household water samples of Bangalore city (Figure 2). These Enterobacteriaceae members are associated with gastroenteritis, salmonellosis and bacillary dysentery. The dominant bacterial species are E. coli, Salmonella, Shigella, Klebsiella and Enterobacter. The pathogenic species of E. coli is divided into six groups based on serological and virulence characteristics.

The heterotrophic count of water samples SSW-1, SSW-8, SSW-9, SSW-10, SSW-19 and SSW-20 showed higher values from 2.1 × 10⁶ to 3.0 × 10⁶ CFU/mL. The higher value of such samples may be due to prolonged storage of water in a pot. Microbiological assessment of the drinking water from the households of Bangalore city demonstrates its vulnerability due to indicator and enteric bacteria. The overall results showed that the consumption of such contaminated water at end-user point may cause potential health hazards to the inhabitants.

The hydrogen ion concentration in all water samples remained alkaline throughout the study period. The average pH of water samples showed a maximum of 8.1 and minimum of 7.5. The pH values of water in all samples were within the permissible limit recommended by WHO (6.5–8.5).

The conductivity of all water samples showed ranges from 400 (μmho) to 1,120 (μmho). Dissolved oxygen (DO) concentration water samples observed were a maximum 7.4 and minimum 6.1. For all water samples, the DO values were within the permissible limit.

The total hardness was found to be 130 mg/L to 275 mg/L. For all water samples, the total hardness is within the permissible limit recommended by CPHEEO (2009), BIS (2012) and WHO (2017).

During the study period, temperature varied from 26 °C to 29 °C. The minimum temperature was recorded with water sample SGW-12 and the maximum with SSW-1, SGW-4, SSW-8 and SSW-20.

In this present study, the water samples contain turbidity value ranges of 0.4 NTU (SSW-11, SSW-17 and SGW-18) to 4.2 NTU (SSW-1). Drinking water is considered to be good quality when it contains turbidity values of 1 or below (Cotruvo 2017). In this study, some sampling stations exceeded the limit of turbidity value WHO (2017).

For the correlation study, a few physico-chemical parameters with microbial parameters to check the inter-relationship of each parameter were used. Statistically, using Pearson's correlation coefficient TCC was found to be positively and significantly related to pH and turbidity. The pH was found to be significantly and positively related to turbidity. Electrical conductivity was found to be significantly and positively related to DO and TH. TCC was negatively correlated to EC, DO and TH. The pH was negatively correlated with EC, DO and TH. EC, DO and TH were negatively correlated with turbidity. The rest of the combinations were not significantly related to each other (Table 3).

In terms of microbial risk, most of the households (80%) are prone to contamination with waterborne pathogens. This clearly indicates the microbial risk of gastroenteritis. Hence, the water is not suitable for drinking purposes without proper treatment or boiling. The study highlighted that certain physico-chemical parameters are within the permissible range of the regulatory authorities, but most of the microbiological parameters of water samples exceeded the permissible limit. The WHO guidelines for bacteriological quality of drinking water require that all water intended for drinking must contain no E. coli or thermotolerant coliforms in any 100 mL sample. In this study, it was concluded that the water to the end-user point is highly contaminated with coliform bacteria.

In this assessment, people are consuming water from two major sources; bore well water and Cauvery water source. Mostly contamination is greater in prolonged storage in containers or pots. The storage practices and handling the water from storage containers at home caused the quality deterioration, posing a potential risk of infection to consumers. Poor personal and domestic hygiene can increase the incidence of waterborne infection. This study concluded that the drinking water to the end-user point is contaminated with the presence of coliform bacteria. The study also revealed that the microbial quality of water from the households was not suitable for drinking purposes without proper treatment or boiling.

All relevant data are included in the paper or its Supplementary Information.