Chemical and Microbiological Quality of Municipal Supply Water in Dhaka South Area, Bangladesh

This project aimed to find out the microbiological quality of municipal supply water in Dhaka South area and if the current regime of microbiological quality testing can determine the risk to public health from supply water satisfactorily. Water samples were collected from six different points of the water distribution network of Dhaka’s south locality, starting from the source (Shitalakhyariver, Narayanganj) to Jagannath University, Dhaka. The dominant taxonomic units were isolated using standard culture techniques, followed by biochemical identification, VITEK2 identification, and biofilm-forming potential of each isolate individually and co-cultured with other isolates. Presumptive identification of isolates from the Shitalakhya River revealed the presence of Citrobacter sp., Alcaligenes sp., and Pseudomonas putida. The sample from Saydabad Water Treatment Plant yielded Vibrio mimicus, Pseudomonas fluorescence, and Alcalimonas. The major aerobic bacteria in the water specimen from the community overhead tank included S aureus, Bacillus cereus, Micrococcus sp., Enterococcus sp., Lactococcus sp. Tap water revealed the presence of Escherichia coli, Lactococcus, Enterobacter, Shigella, Klebsiella, Pseudomonas, and Staphylococcus aureus, as well as anaerobic bacteria. Biochemical tests and VITEK2 yielded different results. Potential biofilm formers such as Klebsiella, E. coli, Enterococcus, Aerococcus, Enterobacter, and Cronobacter indicated quality deterioration potential inside the piped water supply system. Alteration in the major taxonomic units throughout the municipal water distribution network and the presence of opportunistic pathogens and biofilm-formers indicate the necessity for an updated water treatment, quality control, and in-line maintenance system.

Introduction

Access to safe drinking water is one of the most basic universal rights and is included in the “sustainable development goals” (SDG 2030) by the United Nations (UN) (Aroraet al., 2018). A low- and middle-income country like Bangladesh must adhere to SDG 2030 to improve the quality of life for citizens. Bangladesh is a tropical country boasting a population of 170 million people. Rapid urbanization and repeated natural disasters pose challenges to attaining SDGs in Bangladesh.

Dhaka, the capital of Bangladesh, has a population of 20 million people, 83% of whom have access to municipal supply water provided by Dhaka Water Supply and Sewage Authority (DWASA), an agency under the Ministry of Local Government Engineering Department. Dhaka city is divided into 2 municipal areas (Dhaka North and Dhaka South). Dhaka South City has a water supply network established in 1936. This infrastructure acquires natural water from the Shitalakhya River, treats it with chlorination at the Saidabad Water Treatment Plant (WTP), and pumps it to community water pumps, from which it flows to neighborhood overhead tanks. Points-of-uses get municipal water from overhead tanks through the underground piped network. The piped water supply networks were constructed 80 years ago (Khan, 2016), and the microbiological safety test protocol for municipal supply water has been in effect since the 1970s (Baileyet al., 2021). At the moment, DWASA and the Department of Public Health Engineering of the Government of Bangladesh perform routine tests of municipal supply water based on cultural detection of fecal indicator organisms only (Baileyet al., 2021). Public health microbiologists have discovered many microbiological risk factors in supply water to households that were not included in standard protocols in the 1970s, such as opportunistic pathogens, fungi, viruses, parasites, chlorine-resistant pathogens, and biofilm-forming consortia (Edberg, 2000). Microbiological safety and quality assessment of protocol of DWASA was set in 1970s and update is needed to include the emerging risk factors suggested by the World Health Organization (Ahmed, 2021) such as opportunistic pathogens, fungi, viruses, parasites, chlorine-resistant pathogens, biofilm-forming consortia (Edberg, 2000). Biofilms are extremely difficult to remove from the distribution system once they are established, and they can be resistant to disinfectants (Zottola & Sasahara, 1994). Pseudomonas aeruginosa, Legionella, Naegleria, and Mycobacterium spp. are most concerned pathogen that can cause water borne diseases (Zottola & Sasahara, 1994). Ensuring safe drinking water is one of the universal sustainable development ological safety of municipal supply drinking water cannot be ensured without the adoption of modern molecular microbiological safety assays of supply water because culture-based techniques leave out potential pathogens that are either human pathogens or are precursors of deterioration of the quality of drinking water (Bitton, 2014). This report analyses municipal supply water from different locations within the DWASA water acquisition, treatment, and supply system located in Dhaka South area with culture-based as well as VITEK2-based techniques, comparison of culture-based vs. VITEK2-based microbiological reports and risks from biofilm-forming bacteria within the water-supply piped network to stress the requirement to update and revise microbiological test procedure in Bangladesh to make the municipal water safer and better.

The aim of this article was to investigate the physico-chemical and microbiological risk factors present in municipal supply water that could be overlooked by DWASA’s routine test. The objective was to collect water samples from 6 different points from the water sample network (the source, the treatment plant, the pumping station, the overhead tank, the underground reservoir, and the point-of-use tap), compare microbiological qualities of water samples with culture-based analysis vs. VITEK2 based analysis and assess biofilm-forming potential-based analysis that indicates biofouling-forming potential of bacteria present in supply water.

Methods

Sample Collection Process

Water samples were collected from six different locations of the municipal water distribution point of Dhaka WASA. All the samples were collected at regular intervals over a period of five months, from March 2018 to August 2018. Samples were taken to the laboratory within 1 hour for further analysis (Guardabassiet al., 1998). Sample collection activities were done with sterile sampling glass bottles, sample collectors, alcohol thermometers, and ice boxes. The samples were collected with gloved hand and marked immediately after collection with care. The samples were maintained at a cool temperature in a sampling box containing an Ice pack until the samples were taken to the laboratory.

Location and Type of Samples

A total of 6 samples were collected in triplicates from 6 different sites of the water supply system of DWASA (Fig. 1, Table I).

Fig. 1. Locations of sampling sites in Dhaka city, Bangladesh: 1—Shitalakhya River sampling point, 2—Pagla water treatment plant, 3—Jatrabari community pump, 4—LaxmiBazar overhead tank, 5—Jagannath University reservior, 6—point-of-use Department of Microbiology, Jagannath University.

Table I. Location and Sites of Water Sample Collected from Different Points in Dhaka WASA Distribution System

# SI of samling location	Points in the water distribution system	Sites of sample collection
1	Surface water source	Shitalakhya river, Narayanganj
2	Water treatment plant	Pagla Water treatment plant, Jatrabari, Dhaka
3	Community water pumps	Jatrabari pump
4	Community overhead tanks	Laxmibazar tank, Sadarghat
5	Underground reservoir in receiving ends	Undergound reservoir of Jagannath University
6	Taps at points of use	Tap at the Laboratory 1
		Department of Microbiology, Jagannath University, Dhaka

The sampling locations are given below:

• Point 1: Source of surface water from Shitalakhya River.
• Point 2: Jatrabari water supply pump.
• Point 3: Lakshmi Bazar Overhead Tank, which was the nearest tank of Jagannath University.
• Point 4: Overhead tank of Jagannath University, which is situated at the roof of building of Jagannath University.
• Point 5: Underground reservoir in Jagannath University.
• Point 6: the tap water of the Laboratory of the Department of Microbiology, Jagannath University.

Processing of Samples

Approximately 200 ml of water was collected using a sterile reagent bottle tightly wrapped with sterile aluminum foil for the collection of each sample. Tenfold serial dilutions of samples were prepared in physiological saline, and 0.1 ml aliquots were pour-plated on each of the culture media described in the culture media section for the isolation of bacterial colonies.

Culture Media

The following culture media were used for the isolation of waterborne bacterial species: Nutrient agar for total viable count (TVC), McConkey agar for the enteric pathogen, Mannitol salt agar (MSA) for Staphylococcus, membrane fecal coliform agar (mFC) for fecal coliforms, Cetrimide agar for Pseudomonas and Xylose lysine deoxycholate (XLD) for Salmonella and Shigella, thiosulfate citrate bile salt agar (TCBS) for Vibrio and Eosine methylene blue (EMB) agar for E. coli. The findings are presented in Table II.

Table II. Sample Collection from Different Points in DHAKA WASA Distribution System (South)

#SI of sampling sites	Different points of sample collection	Total Heterotrophic Count (THC) (CFU/ml) found in this study	Reference values for acceptable limits of total heterotrophic count for municipal supply water	Number of isolates
			(DPHE, 2016)
1	Shitalakhya river	1.69 × 104	Not specified	6
2	Water treatment plant	4.5 × 104	7 × 105 CFU/ml	5
3	Jatrabari water pump	7.05 × 105	Not specified	5
4	Laxmibazar water tank	5.23 × 105	Not specified	6
5	Jagannath University underground tank	2 × 108	Not specified	6
6	Department of Microbiology,	4 × 104	3.4 × 106 CFU/ml	6
	Jagannath University tap water

Biochemical Tests Methods

The following biochemical media were used for biochemical profiling: Kligler’s Iron Agar (KIA) was used for carbohydrate metabolism, citrate agar for citrate utilization, motility indole agar (MIU) for urease production, indole production and motility, methyl red- Voges-Proskeur media for mixed and volatile acid production, nitrate broth for nitrate reduction, which is presented in Table III.

Table III. Comparison of Identification of Isolates with VITEK2 vs. Biochemical Testing

ID	VITEK2 Identification	Biochemical identification	Source
1	Unidentified	Citrobacter	Shitalakhya river
2	Enterobacter aerogenes	E. coli	Shitalakhya river
3	Enterobacter aerogenes	Unidentified	Shitalakhya river
4	Klebsiella pneumonia subsp. pneumonia	Enterobacter aerogenes	Shitalakhya river
5	Escherichia coli	Unidentified	Jatrabari water pump
6	Cronobacter dublinensis Subsp. dublinensis	Unidentified	Jatrabari water pump
7	Staphylococcus lentis	Unidentified	Jatrabari water pump
8	Aerococcus viridians	Unidentified	Laxmibazar water tank
9	Cronobacter dublinensis subsp. dublinensis	Unidentified	Laxmibazar water tank
10	Enterobacter aerogenes	Enterococcus faecalis	Laxmibazar water tank
11	Escherichia coli	Unidentified	Laxmibazar water tank
12	Cronobacter dublinensis subsp. lactaridi	Micrococcus luteus	Overhead tank
13	Alcaligenes faecalis subsp. faecalis	Bacillus enobaticus	Overhead tank
14	Staphylococcus lentus	Unidentified	Tapwater
15	Unidentified	Shigella dysenteriae	Tapwater
16	Kocuria kristinae	Alcaligenes faecalis	Tapwater
17	Unidentified	Vibrio mimicus	Tapwater
18	Micrococcus luteus	Streptococcus pyogenes	Tapwater

VITEK2 Identification System

The VITEK2 is an automated bacterial identification system utilizing growth-based technology (Biomereux Inc. France). It focuses on the industrial microbiology-testing environment to identify spore-forming Gram-positive bacilli (i.e., Bacillus and related genera). The other colorimetric reagent cards (GN, GP, YST) apply to all system formats for both industrial and clinical laboratories, results are presented in Table III.

Biofilm Assay

Isolates were grown overnight in Luria Broth. The overnight culture was diluted 1:100 with fresh medium into microtiter plates for biofilm assay. A standard biofilm assay medium M63 was supplemented with magnesium sulfate, glucose, and casamino acids. We used triplicate wells for each treatment. After overnight incubation, 125 microliters of 0.1% solution of crystal violet were added in water to each well of the microtiter plate and shaken at room temperature for 10–15 min. The absorbance of individual wells in a plate was quantified with an ELISA reader at 550 nm using 30% acetic acid in water as the blank, which is seen in Table IV.

Table IV. Biofilm Assay and Interactions Observed between Isolates

ID	Isolate	Biofilm-forming potential	Synergistic Biofilm formation with isolates from same sample
2	Enterobacter aerogenes	Yes	Aerococcus viridans
3	Enterobacter aerogenes	No	None
6	Klebsiella pneumoniae subsp. pneumoniae	Yes	Escherichia coli
7	Escherichia coli	Yes	Klebsiella pneumoniae
			Sub sp. Pneumoniae
10	Cronobacter dublinenesis str. lausannensis	No	None
11	Staphylococcus lentus	Yes	Aerococcus viridans
13	Cronobacter dublinenesis subsp. Dublinenesis	No	Enterobacter aerogenes,
			Escherichia coli,
			Cronobacter dublinenesis
			str.lactaridi
15	Enterobacter aerogenes	No	None
17	Escherichia coli	No	None
18	Cronobacter dublinenesis str. lactaridi	Yes	Enterobacter aerogenes,
			Escherichia coli,
			Cronobacter dublinenesis
			Sub sp. Dublinensis
20	Alcaligenes faecalis	No	None
21	Staphylococcus lentus	Yes	None
25	Kocuria kristinae	Yes	None
29	Micrococcus luteus	Yes	None

Finally, the physico-chemical parameters of the water samples were measured with automated probes, such as pH meter (Infitek, USA), conductivity meter (Infitek, USA), alkalimeter (Gaotech, South Korea), Dissoved oxygen sensor (Gaotech, South Korea). Biological oxygen demand (BOD) and chemical oxygen demand (COD) were measured with a 5-day in-house BOD/ COD assay protocol (EPA Standards 5210/5220). Total Nitrogen (TN) was measured with Kjeldahl method (EPA standards 351.2). Total Organic Carbon (TOC), arsenic, iron, sulphur, phosphorous, and lead were measured with methods described in the Handbook of the American Public Health Association (1992) with the help of Bangladesh Council Scientific and Industrial Research (BCSIR).

Results

The Total Heterotrophic Count (THC) rate is different in different sites of the water body. In the Shitalakhya river, from where the raw water is being collected by Dhaka WASA, the THC value is 1.69 × 10⁴ CFU/ml. The THC value of Jatrabari water pump is different from the THC value of Shitalakhya river. The THC range of Jatrabari water pump is 7 × 10⁵ CFU/ml to 2 × 10⁸ CFU/ml. The THC value of the Laxibazar Overhead tank is 2.4 × 10⁸ CFU/ml, which is different from both the Shitalakhya River and the Jatrabari water pump. Lastly, the tap water at point-of-use is also different from all the sites of the water body. The THC value in the tap water supplied by Dhaka WASA is 2.3 × 10⁸ CFU/ml where the reference value is 3.5 × 10⁸ CFU/ml (Table II).

Various bacterial taxonomic units were from different points of Dhaka WASA distribution network (Table III). In the Shitalakhya River, 6 genera were isolated. Among them, 4 were Gram-positive bacteria and 2 Gram-negative (Citrobacter, Alcaligenes) bacteria. In the Jatrabari water pump, a total of 8 isolates were identified: 6 Gram-positive bacteria and 2 Gram-negative bacteria. The Gram-negative bacteria were identified as Pseudomonas and Vibrio. A total of 6 Genera were isolated from the Laxmibazar Overhead tank. Among them, 4 were Gram-positive (S. aureus, Bacillus, Micrococcus, Enterococcus), and 2 were Gram-negative bacteria (Morgan, 1988).

In the Jagannath University reservoir, a total of 6 Genera were identified, where 3 were Gram-positive (Listeria, Lactococcus, and Enterobacter) and the remaining 3 were Gram-negative bacteria. A total of 5 Genera were identified in the tap water at point-of-use: 2 Gram-positive (Staphylococcus, Streptococcus) and 3 Gram-negative bacteria (E. coli, Shigella, and Klebsiella) Percival (1999).

Resistant microbes can survive chlorination and establish complex biofilms inside the supply pipes, deteriorating the quality of supply waters. As evident from Table II, the organisms that establish biofilms successfully inside a municipal distribution system range from pathogens (Aeromonas hydrophila, Salmonella, Klebsiella, Pseudomonas aeruginosa, Legionella pneumophila, E coli), opportunists (Stenotrophomonas moltophilia, Mycobacterium avis complex), toxin producers (Cyanobacteria) to non-pathogens that destroy the pipe material and cause biofouling (Galleonella, Siderooxydans, Geothrix, Nitrospira). The reports from temperate weather show enrichment of molds in the biofilm (Penicillium, Alternaria, Fusarium, Aspergillus, Mucor, Geotrichum, Botrytis) (Hurtado-McCormicket al., 2016). The physico-chemical parameters from water supplied by Dhaka WASA were tested at the Bangladesh Council of Scientific and Industrial Research (BCSIR) (Table V).

Table V. Physico-Chemical Parameters from Water Supplied by Dhaka WASA

Parameter	Tap water	Reference value of WHO	Reference value for Bangladesh	Method
pH	7.5	7	6.5–8.5	pH meter
Conductivity	622 μS/cm	100 μS/cm	500 μS/cm	Conductivity meter
Alkalinity	0	0	0	Alkalimetry
TDS	210 NTU	0	100 NTU	TDS meter
Salinity	230 mg/L	100 mg/L	200 mg/L	EC meter
Hardness	101 mh/L	75 mh/L	75 mh/L	CaCO3
BOD	0.14 mg/L	0	0.03 mg/L	In-house 5 day
DO	7.61 mg/L	0	20 mg/L	DO sensor
COD	3 mg/L	0	4 mg/L	In-house 5 day
TOC	12.19 mg/L	0	0.2 mg/L	APHA 5310B
TN	<5 mg/L	0	1 mg/L	Kjeldahl
Arsenic	<0.005 mg/L	0.01 mg/L	0.05 mg/L	APHA 3114C
Iron	0.62 mg/L	0	0.004 mg/L	APHA 3111B
Sulphate	0.4 mg/L	0	400 mg/L	APHA4100B
Phosphorus	0.5 mg/L	0	6 mg/L	APHA 4500PB
Lead	0.012 mg/L	0	0	APHA 3111B

The pH value of the tap water supplied by Dhaka WASA is 7.5, the reference value of WHO is 7, and the reference value for Bangladesh is 6.5–8.5. The conductivity of the tap water from Dhaka WASA is found to be much higher than the reference value of WHO and Bangladesh. The conductivity level of the tap is 622 μS/cm, where the reference value of WHO and Bangladesh is 100 μS/cm and 500 μS/cm, respectively. No alkalinity is found on the tap water supplied by Dhaka WASA. The alkalinity is 0, where the reference value of WHO and Bangladesh is also 0. An increased level of Total Dissolved Solid (TDS) is found in the tap water of Dhaka WASA. The TDS value is 210 NTU. According to the reference of WHO, the TDS value should be 0, and the perspective of Bangladesh, the value is 100 NTU. An increased rate of salinity is also found in the tap water of Dhaka WASA. The salinity of tap water is 230 mg/L. The reference value of WHO is 100 mg/L, and the reference value for Bangladesh is 200 mg/L. EC meter is used for salinity test. The hardness of the water supplied by Dhaka WASA is 100 mh/L, but the reference value of WHO and for Bangladesh is 75 mh/L. The Biochemical Oxygen Demand (BOD) rate is also higher in the tap water of Dhaka WASA (Md. Sirajul Islamet al., 2020). The BOD rate of the tap water is 0.14 mg/L, which is higher than the preference rate of WHO and Bangladesh. The reference BOD value of WHO is 0, and for Bangladesh, the value is 0.03 mg/L. The dissolved Oxygen rate of the tap water is 7.61 mg/L, where the reference value of WHO is 0, and the reference value for Bangladesh is 20 mg/L. Dissolve Oxygen is being tested by DO sensor. In the case of Chemical Oxygen Demand (COD), the rate found in the COD level in the tap water of Dhaka WASA is 3 mg/L, where the WHO level is 0, and for Bangladesh, the reference value is 4 mg/L. Like BOD, the COD test also takes 5 days.

In the case of Total Organic Compound (TOC), increased rate is being found in TOC level like BOD in the tap water of Dhaka WASA. 12.19 mg/L is found in the tap water, where the reference value for Bangladesh and WHO are 0.2 mg/L and 0, respectively. TN value is below 5 mg/L where the WHO value is 0, and for Bangladesh, the value is 1 mg/L. Arsenic value found in the tap water is below 0.005 mg/L. The maximum tolerance value according to WHO is 0.01 mg/L, and for Bangladesh, it is 0.05 mg/L. Increased Iron level is being found in the tap water of Dhaka WASA. The rate of Iron is 0.62 mg/L. According to the reference of WHO, the maximum value of Iron should be 0, and the perspective of Bangladesh, the value is 0.004 mg/L. Sulphate rate in the Dhaka WASA tap water is 0.4 mg/L. The reference value of WHO is 0, and the reference value for Bangladesh is 400 mg/L. Phosphorus rate of the tap water of Dhaka WASA is in a suitable level. 0.5 mg/L Phosphorus is found in the tap water where the reference rate of WHO and Bangladesh is 0 and 6 mg/L, respectively. In the case of Lead, the reference value of WHO and for Bangladesh is 0, where 0.012 mg/L Lead is being found in the tap water supplied by Dhaka WASA.

Discussion

Opportunistic waterborne pathogens include Mycobacterium avium complex, Stenotrophomonas maltophilia and Aeromonas hydrophila that can infect immune-compromised groups such as infants, adults, pregnant women and people with underlying medical conditions (cancer, HIV/AIDS etc). M. avium causes pulmonary, soft tissue and lymph node infections (Tortoli, 2009). Stenotrophomonas maltophilia causes respiratory infection in cystic fibrosis patients. Aeromonas hydrophila is an enteric pathogen infecting children and immunocompromised people (Maniet al., 1995). The aquatic biofilms have also been implicated in spread of drug-resistance genes (Talukdaret al., 2013) had shown presence of extended spectrum beta-lactam (ESBL) E. coli and QnrS elements for quinolone resistance from tap water in Dhaka city. Biofilm microbes also produce metabolites and components that change the quality of drinking water. Aspergillus spores are allergenic (Lowet al., 2011). The odor in tap water often results from dimethyl polysulphides, produced by Pseudomonas, Flavobacterium, Aeromonas, and Penicillium (Schulz & Dickschat, 2007) All these information stress on the development of robust and sensitive analytical techniques for evaluation of water quality as well as revised maintenance procedures that would help reduce formation of biofilms inside municipal water distribution pipes.

Over the last decade, the original report of microbiological analysis of tap water from Bangladesh mentioned isolating viable cells of coliforms and E. coli (Uddinet al., 2018). Klebsiella, Salmonella, Shigella, Vibrio, Aeromonas, and fungi, literature search on interaction of each pair of these microorganisms in a dual-species interaction helps to construct a hypothetical network of microbes in the water supplied by WASA. Aeromonas hydrophila showed positive interaction with Salmonella spp and Listeria monocytogenes (Allen & Poppe, 2002) but is inhibited by Pseudomonas aeruginosa at the planktonic phase of biofilm development (Lynch & Robertson, 2008). It has been found that live bacteria in more than 60% of the sampled tap water, which exceeds the Bangladesh Standards (BDS 1240:2001) for the microbiological quality of water. The Bangladesh Department of Public Health and Engineering (DPHE) has set different set of standards for potable water in Bangladesh, which vary from the universal standards set by the World Health Organization (WHO) in many parameters. Coliforms and E. coli are frequently reported in supply water (Acharjee, 2011; Mahmud, 2019) had reported finding E. coli, Klebsiella, Salmonella, Shigella, Vibrio, Aeromonas, and fungi from supply water, indicating that these bacteria and molds survive disinfection procedures. When taken together with the quality of raw water with higher concentration of Iron and Arsenic, we find factors limiting certain kinds of microbes in the distribution system. If we summarize the parameters reported from independent original studies, we can set the parameters of the supply water within the reported ranges. The pH of the natural water varies between 7–8, and the dissolved Oxygen ranges between 3–5 mg/L. The conductivity of the waters is 1158 μS/cm, much higher than the reference value for natural waters (Cole, 1982). The turbidity of the water is 1.1 NTU. The nitrate concentrate was 8.5 mg/L, closer to the upper limit of nitrate concentration (Acharjee, 2011). The Iron concentration was 0.05 mg/L, and phosphate and sulphate concentrations were 4.4 mg/L and 9 mg/L, respectively. The tap water for domestic use contained 0.02 mg/L of residual Chlorine (DPHE, 2010).

According to Zhouet al.(2020) the turbidity, ammonia concentration, nitrate content, and total organic Carbon content of the water inside the supply system influence the nature and extent of biofilm formation. Keet al.(2023) reported that the seasonal cycling of the biofilms inside the pipes correlated with seasonal temperature fluctuations. Bacteria that survive and develop biofilms under these conditions would be E. coli, Shigella, Vibrio, Klebsiella, Salmonella, Legionella pneumophila, Flavobacterium, Sphingomonas, Pseudomonas aeruginosa, Nitrospira, Actinobacterium, Acidobacterium, Aeromonas, Sphingobacterium, Mycobacterium avium, Bacteroidium, Clostridia, Spirochaetes, Acremonium, Cladosporium, Fusarium, Microbacterium, Stenotrophomonas (Amendet al., 2013; Sanders, 1997).

Temperature, pH, conductivity, turbidity, dissolved Oxygen, type, and amounts of minerals, total organic Carbon, total Nitrogen, and biological/ chemical oxygen demands are the non-biologic parameters that set the limits for microbial life (Moazeniet al., 2013). The microbes form and thrive in a biofilm through biomass transfer from the organic Carbon and microbial growth on any solid support. These studies carried out between 2002 and 2017 in Europe, the US, Australia, China, Korea, and Brazil show varied types of microbial populations in biofilms (Morgan & Davies, 1999). The summer temperature in Europe and North America is around 15 °C to 25 °C, and the natural population of the surface waters is diverse genera of bacteria, fungi, and molds (Leeuwen, 2000). The total organic carbon (TOC) content was stated to be 8.5 mg/L in one of the reports (Proshad, 2021). The water distribution pipes are composed of a wide range of materials depending on the soil type, depth, water pressure, flow and retention pattern, the intended life of the pipes, etc. While UV radiation does not produce residual effect, chlorination is allowed to leave a threshold of 5 mg/L residual free chlorine so that any remaining pathogens are gradually killed on their way to the receiving end.

Conclusion

The multi-faceted problem of biofilms inside the municipal water distribution pipe has not yet been addressed in Bangladesh. Microbial interactions subject urban consumers to an even larger threat of an antimicrobial resistance epidemic. The incidences of water-borne infections and occasional deterioration in the quality of supply waters (odor, discoloration) call for cutting-edge, in-line, real-time monitoring facilities with prompt interventions (Zimmermannet al., 2014). Biological active Carbon (BAC) filters, granular active carbon (GAC) filters, UV lights, contact chlorine treatment, and engineered storage and distribution might prove useful in improving water quality and safety.