The statistical summary of water quality parameters and their comparison with their permissible limits with percentage of samples deviated from permissible limit as per IS 10500 (2012) has been shown in Table 2. The water quality parameters in Table 2. have been plotted for three different zones using Box-whisker plot are illustrated in Figs. 2(a), (b), (c), (d), (e), (f), (g), (h), (i), and (j).
From the Table (2) and Fig. 2(a) it has been found that the Bhubaneswar piped supply water has a pH that ranges from 5.56 to 8.61 in both north zone and south- west zone while it is 6.23 to 8.59 in south-east zone. The average values of all the three zones are 7.66, 7.73 and 7.56 respectively, which indicates that the supply water is slightly alkaline. According to Sajil Kumar et al. (2013), hydroxides, carbonates, and bicarbonates primarily regulate the alkalinity of groundwater. It has been marked that the piped supply water samples exceeding beyond the permissible limit are 11.65% in north zone, 13.33% in south west zone and 6.4% in south east zone respectively. The standard deviation is 0.48 to 0.70 which indicates the value clustered tightly to the mean. Figure 3 represents the areas which are more affected in pH are Damana Area of ward No8 and Indradhanu market area of ward no 27 whose pH values are 8.61. Also, the areas which are acidic water has been detected in areas like Sriram Nagar of ward no 59, Swadhin Nagar of ward no 34 and Pancha Sakha Nagar of ward no 64 whose pH values are 5.56 ,5.74 and 5.56 respectively. It shows that the areas which are affected by this variation of pH are expected due to the factors like old age of supply pipes more than 40 years and also due to lack of maintenance.
One significant indicator of water quality and organic pollution in bodies of water is dissolved oxygen (DO). Dissolved Oxygen has the average value 7.5, 7.54 and 7.43 in north, south west and south east zone respectively. There is a deviation of DO values of 20.38%, 21.9% and 15.2% samples from the permissible range in the zones of North, South-west and South-east respectively as shown in Table.2. Also, it is found that there are some areas having DO values less than 6 mg/l, such as Sikharchandi Nagar of Word no 2, Shakti Vihar of ward no 20, Shree Vihar of ward no 22, Dumduma Phase 3 of ward no 64, Jharapada high school area of ward no 42 as presented in Fig. 4. Ordinarily, polyphosphates are coated inside municipal water supply pipes to shield the metal from oxygen exposure and thus results in high DO concentrations.
We understand that the electrical conductivity of water decides the minerals and salts that are dissolved in the water. Electrical Conductivity (EC) is from 58.25 µs/cm to 480 µs/cm in north zone, 67.7 µs/cm to 519.9 µs/cm in south west zone and 173 µs/cm to 581.47 µs/cm in south east zone of Bhubaneswar respectively. As per Fig. 5 it is observed that in north zone 8.73% samples, 4.76% in south west zone and 17.6% in south east zone are beyond the permissible limit. There are some areas having conductivity higher than 500 µs/cm are Sir Pu Bhoi Sahi of ward no 51, Nico Park Lake area of ward no 28, Bhoi Sahi of Ward no 28, Gridco Colony of ward no 29, Sarala Nagar and Santoshi Nagar of Ward no 31 shown in Fig. 5. Runoff water, septic systems, animal wastes and sewage leaking into the ruptured old pipeline system are the probable causes of unusual level of electrical conductivity.
As per Fig. 2. (d), the data have been presented in graphical form with the help of box and whisker plot graph. The median of the lower half of the data set is known as the first quartile (Q1). The midway number of a data collection that splits it into two equal sections is called the median which is represented as Q2 and the median of the upper half of the data is known as the third quartile (Q3). In north zone the first quartile (Q1) is 43.2, the median is 58.96, and the third (Q3) is 68.7. For south west zone Q1 is 53.4, Q2 is 59.64 and Q3 is 64.3. For south east zone Q1 is 43.05, Q2 is 45.7 and Q3 is 47.85. From the graph it can be concluded that north zone has a large variation i.e. 25–75% areas deviated with high alkalinity values as compared to south west zone and south east zone. As per Fig. 6, it has been found that no areas are affected by alkalinity.
Chloride is non-reactive by nature; it typically enters supply water systems through soil erosion caused by potash fertilisers and animal and human waste (Yousuf et al. Citation 2012). As per Fig. 2(f) in North zone the mean is 33.86 mg/l, 34.29 mg/l in south west zone and 38.84 mg/l in south east zone. The standard deviation of Chloride is 11.65 for north zone, 10.76 for south west zone and 7.61 for south east zone. As per Fig. 8, there is no sign of deviation from the permissible limit.
As per Fig. 2 (h), the mean value in the three zones varies from 2.39 to 2.75. This indicates a relatively consistent range of values across the zones. Additionally, according to Fig. 10, all of the BOD (Biochemical Oxygen Demand) values fall within the allowed range. This suggests that the water quality in the measured zones meets the specified standards or regulatory requirements, affirming the overall environmental health in those areas."
As per IS-10500-2012, the range for Sulphate is 200 mg/l. Beyond 400 mg/l the water is harmful and cause disease if used for consumption. The dissolution of minerals, atmospheric deposition, and various human sources (fertiliser, mining, etc.) are the sources of sulphate. The high sulphate levels found in many global aquifers are largely due to gypsum. The average value ranges between 15.57 mg/l to 17.14 mg/l in the three zones of Bhubaneswar. Figure 11 represents that no sulphate content is present in Bhubaneswar.
According to IS10500-2012, the nitrate range is 45 mg/l, which is the desired level, and all the samples are with in the limit. Maximum value observed is 30 mg/l in both south east zone and south west zone which is presented in the Fig. 2 (j). The high rates of precipitation that promote fertilizer infiltration are responsible for the high NO3− values in the source of supply water (Wagh et al. 2017b, 2018b). High concentration in nitrate causes blue baby syndrome. Figure 12 indicates that Bhubaneswar supply water is safe from Nitrate contamination.
3.1 Water Quality Index and its Analysis
Table 3
Water quality Index status of supply water in different zones of Bhubaneswar
Water Quality Status | North zone | South-west zone | South-east zone |
Excellent Water Quality | 23.81% | 9.53% | 28.58% |
Good Water Quality | 76.19% | 90.47% | 71.42% |
Poor Water Quality | - | - | - |
Very Poor Water Quality | - | - | - |
Unsuitable for Drinking | - | - | - |
From Table 3. it can be observed that water quality is of excellent and good condition has been found in the supply water of north, south-west and south-east zone of Bhubaneswar. Highest percentage of excellent water quality has found in south-east zone of Bhubaneswar i.e. 28.58%, while lowest percentage has found in south-west zone i.e. 9.53%. Highest percentage of good water quality i.e. 90.47% has found in south west zone of Bhubaneswar. While north zone and south east zone shows 70–80% of good water quality index. No sign of poor, very poor and unsuitable water quality index has found in all the three zones of Bhubaneswar.
It is evident from Fig. 13 that certain regions of Bhubaneswar have good drinking behaviour scores in terms of water quality index. One outlier is formed with a value of 11 belongs to ward no. 17 of north zone of Bhubaneswar which is highly deviated from the normal values. North zone shows median 30.4, south-west zone shows median 33.2 and south west zone shows median value 28.5 which indicates that on an average south west zone has better water quality as comparison with other two zones.