Drinking Water Quality Assessment: A Study of Evaluate Ground Water Quality at Koyra

Upzilla in Khulna, Bangladesh.

Summary

In the last few decades population of Bangladesh has been increased multiple times. Due to this

increasing population pressure with effects of rapid land use changes on shallow groundwater

quality, an attempt in this study was made to determine and thereby, assess shallow groundwater

chemistry and quality in an Upzilla (sub-district) of Bangladesh. Samples from 15 tube wells

were collected and compared with Bangladesh drinking water quality standards and with the

WHO recommended adequate limit standards. The analysis shows that most of the water sample

did meet neither the standards of Bangladesh drinking quality nor the WHO standards. Finally,

this study gives a guideline to the policy maker in managing water resources in the study area.

Keywords: tube well, shallow groundwater, drinking water quality, coastal area, Bangladesh,

brackish,

Background:

Bangladesh is the largest delta in the world (Chowdhury et al. 2012 in Islam & Ahmed n.d.). It

occupies the major part of the delta of the Ganges-Brahmaputra-Meghna (GBM) river system

and lies mostly within the Bengal Basin (Frenken ed. 2012). The land structure, underlie most of

Bangladesh, is mostly made of unconsolidated Pleistocene fluvial, fertile aquifer and estuarine

sediments and most of the water withdrawn primarily from these quaternary strata (Zahid &

Ahmed 2006). Ever since in 1960's, when agricultural activities boomed and turned into the main

profession of the people of this country, groundwater has been used extensively as the primary

source of drinking and irrigation water supply (ibid). According to Rahman & Parvin (2009)

about 77 percent of cultivated land is irrigated by groundwater through Shallow Tube Wells

(STWs) and the remaining 23 percent by surface water. Again among all the withdrawn

groundwater, only 10-30 percent is used for drinking and other uses and rest of the 70-90 percent

is being used for agricultural purposes (Zahid & Ahmed 2006). Because of increasing population

pressures with effects of rapid land use changes shallow groundwater quality (ibid). In this study,

an attempt was be made to determine and thereby, assess shallow groundwater chemistry and

quality in a south-western coastal area of Bangladesh. For this study, shallow ground waters

from 15 tube wells will be collected and analyzed for major ions1 following standard methods.

1 There are 7 common ions in freshwater: cations: Ca+2 , Mg+2 , Na+1 , K+1 anions: Cl-1 , SO4 -2 , HCO3-1

The suitability of shallow ground waters for drinking purpose was also evaluated by comparing

with standard values. Finally, the paper shows some evidence in support of the argument that,

not only does an evaluation of shallow groundwater quality fundamental to secure human

consumption of groundwater, but it can play a central role in managing the groundwater

resources of coastal areas.

Study Area and Methodology:

Study Area:

The study will be conducted in Koyra Upazila, which is a south-western coastal area of

Bangladesh (Fig. 1).

FIGURE 1: Study area showing location of tube wells sampled for groundwater analyzes

Koyra is a sub-district (Upazila) of Khulna and located at 22.3417°N 89.3000°E. With an area of

1775.41 sq km, it is bounded by Paikgachha Upazila on the north, the Bay of Bengal and the

Sundarbans on the south, Dacope Upazila on the east, Assasuni and Syamnagar Upazila on the

west (Kalaroa - SATKHIRA n.d.). The area is very close to the Bay of Bengal and the

Sundarbans mangrove forest to the south. The landforms of the study area characterized by the

Ganges-tidal floodplain having lower reliefs with the flat surface and crisscrossed by

innumerable tidal rivers and channels. The surface geology of the study area consists mainly of

Quaternary sediments (Rashid 1977; Brammer 1996; Takagi et al. 2005; Ahmed & Falk 2008).

Upper shallow unconfined aquifers characterize the geological formation of groundwater in the

study area, middle confined aquifers, and deep confined aquifer and among the aquifers the

upper shallow unconfined aquifers of the study area are mainly used for drinking and irrigation

purposes (UNDP 1982). The monthly average maximum temperature of up to 36ºC from 2000 to

2010 recorded in the study area, whereas the monthly average minimum temperature recorded

about 10ºC from 2000 to 2010 and the average minimum rainfall from 2000 to 2010 is about

1760 mm/yr (BBS 2011; Azam 2011).

Sampling and Analysis Method

A sample from 15 shallow production wells penetrating the shallow alluvial aquifers in the study

area was collected. The shallow groundwater analyzed for Na+, K+, Ca2+, Mg2+, HCO3-, Cl-,

SO42, NO3-, PO43- and H4SiO4. The depths of wells obtained from the Department of Public

Health and Engineering (DPHE) officials, and the well owners’ records and the acceptable

depths of the wells will be ranged from 50 to 300 feet. Water sample bottles rinsed several times

(at least twice) with sample water, and the tube wells pumped ground water out of the wells

sufficiently at least ten minutes to ensure that the groundwater samples can be representative of

the study area. Then, temperature, pH, EC and TDS was right away measured in the field by a

portable pH (HANNA) meter and an EC/TDS meter (HANNA). Rest of water analysis

(measuring the ion level) was done in the laboratory less than four degree Celsius temperatures

and world standard scale used to determine the water quality parameters (APHA 1995).

However, the suitability of shallow groundwater for drinking purpose was evaluated by Physico-

chemical characteristics of the shallow groundwater as it similarly assessed in different water

quality literature (e.g., Rani & Babu 2008; Adhikary et al. 2012). Lastly, a comparison was done

between Bangladesh drinking water quality standards (Ahmed & Rahman 2000) and WHO

standards (WHO 1993) to calculate the suitability of shallow ground waters for drinking purpose.

RESULTS AND DISCUSSION

Quality of Groundwater:

For the evaluation of the quality of ground water, it is needed to understand its chemical

composition. The Physico-chemical compositions of the shallow groundwater of all samples are

presented in Table 1.

Then, the summary of descriptive statistics for the analyzed Physico-chemical parameters is

shown in Table 2 and Fig 2. Electro Neutrality (EN) Values were used to analysis the water

quality. The value calculated from the equation –

{(TZ+-TZ-)/(TZ++TZ-)}×100

Here, TZ+ and TZ- are the total cations and the total anions in meq/L respectively. In all

samples, the calculated EN values were less than 5% confirming the reliability of the analytical

results (Datta & Subramanian 1997).

Water Type and its Physico-chemical Situation

The groundwater chemical composition controlled by both natural and anthropogenic factors and

thus, the Physico-chemical groundwater quality varies spatially (Balathandayutham et al. 2015).

It found that pH of the shallow groundwater varies from 6.10 to 6.49 with a mean value of 6.3,

and this result indicates that the shallow groundwater is slightly acidic in nature that may be due

to the leaching of organic acids from the upper surface into the lower unconfined shallow

aquifers of the area. The total dissolved solids (TDS) of the shallow groundwater range from 444

to 3487 mg/L with an average value of 2129 mg/L and this indicates that the shallow

groundwater enriched with high soluble salts. As the examined area is near to the sea, and there

is a high frequency of saline water entrance into the shallow alluvial aquifers of the area

indicating an indication of the deterioration of shallow groundwater quality in the area. However,

by the classification of groundwater proposed by Freeze and Cherry (1979) most of the shallow

groundwater (about 87%) in the study area are brackish in nature indicating unsuitability for

human consumption as shown in Table 3.

TABLE 1: Groundwater Chemistry of the Study Area

Sample ID Depth

(ft)

Temperature

(ºC)

pH TDS

(mg/L)

EC

(µS/cm)

Na+

(mg/L)

K+

(mg/L)

Ca2+

(mg/L)

Mg2+

(mg/L)

HCO3-

(mg/L)

Cl-

(mg/L)

SO42-

(mg/L)

NO3-

(mg/L)

PO43-

(mg/L)

SiO2

(mg/L)

Tube Well

(STW)

STW1 160 28.1 6.1 2359.18 5321 383.12 12.13 248.58 89.28 695.56 913.45 8.97 0.061 0.029 5

STW2 315 28.2 6.13 1791.94 4820 294.88 9.71 203.39 77.92 506.61 684.45 2.82 0.084 0.072 7.5

STW3 152 28 6.31 661.21 982 28.25 2.81 94.18 32.81 455.81 35.45 0.63 0.075 0.098 6.94

STW4 97 28 6.35 443.94 709 43.36 4.01 68.12 9.44 218.64 87.45 4.3 0.057 0.062 5.31

STW5 60 28.1 6.44 1868.69 3410 321.32 5.45 189.13 31.6 755.27 538.1 16.22 0.064 0.034 7.19

STW6 60 28.1 6.23 2707.1 6700 717.75 13.73 176.43 14.03 721.47 1037.05 17.2 0.097 0.042 5.81

STW7 150 28.1 6.27 3474.74 8900 811.23 20.24 273.23 23.68 940.03 1380.35 9.56 0.074 0.044 10.19

STW8 220 28.1 6.49 3487.76 9330 1078.4 14.15 184.26 16.31 709.58 1468.8 3.94 0.049 0.068 7.63

STW9 315 28.1 6.24 3442.81 8770 941.8 19.42 162.12 10.08 878.5 1418 4.7 0.057 0.029 5.06

STW10 155 27.9 6.27 1133.19 2540 154.4 13.37 143.35 27.4 441.2 336.3 3.19 0.051 0.029 8.69

STW11 37 28 6.28 1909.35 3800 323.8 15.8 168.33 56.99 604.18 714.45 15.83 0.124 0.05 6.13

STW12 135 28.2 6.45 1660.85 3140 275 14.99 176.13 43.47 673.36 460.85 4.56 0.065 0.022 7.75

STW13 200 28.2 6.31 2913.68 7510 574.43 13.57 212.41 92.66 821.47 1182.55 4.43 0.127 0.029 7.5

STW14 145 28.2 6.39 1996.72 4370 357.18 11.13 189.3 48.61 659.85 703.9 15.55 0.037 0.059 6.94

STW15 150 28.2 6.3 2088.58 4740 371.61 19.83 142.21 83.3 660.9 788.9 15.92 0.082 0.029 3.63

TABLE 2: Summary of Groundwater Chemistry of the Study Area

Statistical

parameter

Temperature

(ºC)

pH TDS

(mg/L)

EC

(µS/cm)

Na+

(mg/L)

K+

(mg/L)

Ca2+

(mg/L)

Mg2+

(mg/L)

HCO3-

(mg/L)

Cl-

(mg/L)

SO42-

(mg/L)

NO3-

(mg/L)

PO43-

(mg/L)

SiO2

(mg/L)

Mean 28.1 6.3 2129 5003 428.9 12.7 175.4 43.8 649.4 783.3 8.5 0.074 0.046 6.7

Maximum 28.2 6.49 3487 9330 1293.7 20.24 273.2 92.66 940.03 1468.8 17.2 0.13 0.098 10.19

Minimum 27.9 6.1 444 709 28.3 2.81 68.1 9.44 441.2 35.5 0.63 0.037 0.05 3.36

Standard

deviation

0.15 0.12 1058 2576 318.8 6.3 59.6 25.99 59.5 467.4 4.6 0.028 0.019 1.96

Coefficient of

variation

0.55 1.82 49.23 60.19 74.32 39.95 37.38 59.68 23.6 63.7 68.1 38.46 45.14 26.89

2

2 Here,

1. The blue line denotes mean value and diamond in the line indicate mean values for each parameter.

2. The red line shows maximum value and square in the line show maximum values for each parameter.

3. The green line denotes minimum value and triangle in the line indicate minimum values for each parameter.

4. The purple line means standard deviation and cross in the line indicates standard deviation for each parameter.

5. The sky blue line denotes coefficient variation and star in the line indicate coefficient variation for each parameter.

-2000

0

2000

4000

6000

8000

10000

0 2 4 6 8 10 12 14 16

Mean

Maximum

Minimum

Standard deviation

Coefficient of variation

Linear (Mean)

Linear (Maximum)

Linear (Minimum)

Linear (Standard deviation)

Linear (Coefficient of variation)

1

1

2

3

4

5

2

3

5

4

FIGURE 2: Summary of Groundwater Chemistry of the Study Area

TABLE 3: Classifications of Shallow Groundwater of the Study Area

TDS (mg/L) Groundwater type Number of samples

within the type

Percentage of

groundwater samples

<1,000 Freshwater type STW3;STW4 13.3

1,000-10,000 Brackish water type STW1;STW2;STW5-

STW15

86.7

10,000-100,000 Saline water type Nil Nil

>100,000 Brine water type Nil Nil

Drinking Water Quality

It found that that 83.3% of the groundwater samples have exceeded the WHO recommended

acceptable limits for drinking water on pH, TDS, Ca2+, Mg2+, and Clˉ (WHO 1993). Whereas,

75.1% of the shallow ground waters have exceeded the Bangladesh recommended limits, based

on Ahmed and Rahman (2000), of pH, Na+, K+, Ca2+, Mg2+ and Clˉ in Koyra Upzilla.

However, the study clearly indicates that most of tube well water in the study area is not suitable

for consumption purpose. This unsuitability cause due to its geographic location near to the sea

and due to sea water intrusion into the shallow alluvial aquifers of the area resulting in Na+ and

Clˉ concentrations in shallow alluvial aquifers of the southwestern coastal area of Bangladesh

(Zahid et al. 2008).

FIG 2: Summary of Groundwater Chemistry of the Study Area

Table 4: Comparison of water samples with WHO standards and undesirable effects

Physico-

chemical

parameter

WHO (1993) Percentage

of samples

Exceeding/

below

desirable

limit

Percentage

of samples

exceeding

maximum

allowable

limit

Undesirable effects if

maximum limit exceeded Desirable

limit

Maximum

allowable

limit

pH 7.0-8.5 9.2 100 Nil Undesirable taste

TDS (mg/L) 500 1500 93.3 86.7 Gastrointestinal irritation

Na+

(mg/L) -- 200 -- 80 --

K+ (mg/L) -- 12 -- 73.3 Bitter taste

Ca2+

(mg/L) 75 200 93.3 13.3 Scale formation

Mg2+

(mg/L) 50 150 46.6 Nil --

Clˉ (mg/L) 200 600 20 66.66 Salty taste

SO42ˉ(mg/L) 200 400 Nil Nil Laxative effects

NO3- (mg/L) 45 - Nil -- Blue baby disease

Table 4: Comparison of Tube well water samples with Bangladesh standards

Groundwater quality parameter Unit Ahmed and

Rahman

(2000)

Percentage of samples

Exceeding/below allowable

limits

Bangladesh

standard

pH - 6.5-8.5 100

Na+ mg/L 200 80

K+ mg/L 12 73.33

Ca2+

mg/L 75 93.33

Mg2+

mg/L 30-35 86.6

Clˉ mg/L 150-600

80

PO43-

mg/L 6 Nil

SO42ˉ mg/L 400 Nil

Conclusion:

From the analysis, it is clearly

evident; water quality in the study area does not meet the drinking water standard. It also shows

that shallow groundwater chemistry reveals that the groundwater compositions are highly

enriched with dissolved solids. The results have shown that 83.3% of the shallow groundwater

have exceeded the WHO recommended desirable limits for drinking water, whereas 75.1% have

exceeded the Bangladesh recommended limits, and this indicates that most of the shallow

groundwater in the study area are unsuitable for human consumption. Moreover, almost every

water source in the study area is brackish in nature, and saline water intrusion is the main

geochemical factor causing deterioration of the groundwater quality in the study area. So, in

future before taking any developmental initiatives, this insight would be a guideline to policy

makers for managing groundwater resources in the study area as well as another saline invades

areas of Bangladesh.

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