Corrosion and scaling is a major problem in water distribution systems, thus evaluation of water corrosivity properties is a routine test in water networks. To evaluate water stability in the Bandar Abbas water distribution system, the network was divided into 15 clusters and 45 samples were taken. Langelier, Ryznar, Puckorius, Larson–Skold (LS) and Aggressive indices were determined and compared to the marble test. The mean parameters included were pH (7.8 ± 0.1), electrical conductivity (1,083.9 ± 108.7 μS/cm), total dissolved solids (595.7 ± 54.7 mg/L), Cl (203.5 ± 18.7 mg/L), SO4 (174.7 ± 16.0 mg/L), alkalinity (134.5 ± 9.7 mg/L), total hardness (156.5 ± 9.3 mg/L), HCO3 (137.4 ± 13.0 mg/L) and calcium hardness (71.8 ± 4.3 mg/L). According to the Ryznar, Puckorius and Aggressive Indices, all samples were stable; based on the Langelier Index, 73% of samples were slightly corrosive and the rest were scale forming; according to the LS index, all samples were corrosive. Marble test results showed tested water of all 15 clusters tended to scale formation. Water in Bandar Abbas is slightly scale forming. The most appropriate indices for the network conditions are the Aggressive, Puckorius and Ryznar indices that were consistent with the marble test.

INTRODUCTION

Corrosion and scaling are major problems in water distribution systems that may cause economic problems, and hydraulic, aesthetic and health effects (Edwards 2004). Corrosive water can react with household plumbing and metal fixtures resulting in the deterioration of the pipes and increased metal content of the water. Consumption of water with elevated levels of toxic metals, such as lead and copper, has been shown to cause both acute and chronic health problems. In addition, taste and odours, as well as the appearance of delivered water, are adversely affected. The scale could clog or reduce the flow in pipes, cause build-up in hot water heaters and reduce their efficiency, and impart an alkali taste to the water (Demadis 2004, Demadis et al. 2007; Edwards 2004).

Factors influencing the release of corrosion scale materials derive from a wide variety of issues associated with water chemistry, biological processes, composition of pipe scale and the hydraulic flow characteristics within the pipe. Chemical properties related to corrosion and scale formation of water include pH, alkalinity, dissolved oxygen content and total dissolved solids (TDS). The main physical characteristics are temperature, flow and velocity of water (Peng et al. 2010).

In general two approaches have been used to evaluate the corrosion and scale-forming tendency of water: direct laboratory methods and mathematical indices. The indices include the Langelier saturation index (LSI), Ryznar stability index (RSI), Puckorius scaling index (PSI), Larson–Skold index (LS) and aggressive index (AI) (Omar et al. 2010; Slavíčková et al. 2013). Details of these indices are presented in Table 1 (Omar et al. 2010; Li et al. 2012; Lianga et al. 2013). As is clear from Table 1, saturated pH, an important factor in determining corrosion or scaling of water, is affected by the chemical and physical properties of water given in Table 2.

Table 1

Corrosion and saturation indices used in the study (Antony et al. 2011)

Index Equation Index value Water condition 
Langelier saturation index LSI = pH − pHs 0 > LSI Super-saturated, tend to precipitate CaCO3 
0 = LSI Saturated, CaCO is in equilibrium 
0 < LSI Under-saturated, tend to dissolve solid CaCO3 
Ryznar stability index RSI = 2pHs − pH 6 > RSI Super-saturated, tend to precipitate CaCO3 
6 < RSI < 7 Saturated, CaCO is in equilibrium 
RSI > 7 Under-saturated, tend to dissolve solid CaCO3 
Puckorius scaling index PSI = 2 (pHeq) −pHs
pHeq = 1.465 × log10[alk] + 4.54
pH = 1.465 + log(T.ALK) + 4.54 
PSI < 6 Scaling is unlikely to occur 
PSI > 7 Likely to dissolve scale 
LS index LSI = (Cl + SO2−)/(HCO3 + CO32−LS < 0.8 Chloride and sulphate are unlikely to interfere with the formation of protecting film 
0.8 < LS < 1.2 Corrosion rates may be higher than expected 
LS > 1.2 High rates of localized corrosion may be expected. 
Aggressive index AI = pH + log[(alk)(H) AI > 12 Non-aggressive 
10 < AI < 12 Moderately aggressive 
 Very aggressive 
Index Equation Index value Water condition 
Langelier saturation index LSI = pH − pHs 0 > LSI Super-saturated, tend to precipitate CaCO3 
0 = LSI Saturated, CaCO is in equilibrium 
0 < LSI Under-saturated, tend to dissolve solid CaCO3 
Ryznar stability index RSI = 2pHs − pH 6 > RSI Super-saturated, tend to precipitate CaCO3 
6 < RSI < 7 Saturated, CaCO is in equilibrium 
RSI > 7 Under-saturated, tend to dissolve solid CaCO3 
Puckorius scaling index PSI = 2 (pHeq) −pHs
pHeq = 1.465 × log10[alk] + 4.54
pH = 1.465 + log(T.ALK) + 4.54 
PSI < 6 Scaling is unlikely to occur 
PSI > 7 Likely to dissolve scale 
LS index LSI = (Cl + SO2−)/(HCO3 + CO32−LS < 0.8 Chloride and sulphate are unlikely to interfere with the formation of protecting film 
0.8 < LS < 1.2 Corrosion rates may be higher than expected 
LS > 1.2 High rates of localized corrosion may be expected. 
Aggressive index AI = pH + log[(alk)(H) AI > 12 Non-aggressive 
10 < AI < 12 Moderately aggressive 
 Very aggressive 
Table 2

Values of (A, B, C and D) for pHs calculation (Dąbrowski et al. 2010)

TDS (mg/L) CaH (mg/L CaCO3)a Alk (mg/L) CaCO3) 
50–300 0.1 10–11 0.6 10–11 
400–1,000 0.2 12–13 0.7 12–13 1.1 
Temperature (°C) 14–17 0.8 14–17 1.2 
18–22 18–22 18–22 1.3 
23–27 23–27 27–23 1.4 
28–34 1.1 28–35 1.5 
0–1 2.6 35–43 1.2 36–44 1.6 
2–6 2.5 44–55 1.3 45–55 1.7 
7–9 2.4 56–69 1.4 56–69 1.8 
10–13 2.3 70–87 1.5 70–88 1.9 
14–17 2.2 88–110 1.6 89–110 
18–21 2.1 111–138 1.7 111–139 2.1 
22–27 139–174 1.8 140–176 2.2 
28–31 1.9 175–220 1.9 175–220 2.3 
32–37 1.8 230–270 230–270 2.4 
38–43 1.7 280–340 2.1 280–350 2.5 
44–50 1.6 350–430 2.2 360–440 2.6 
51–55 1.5 440–550 2.3 450–550 2.7 
56–64 1.4 560–690 2.4 560–690 2.8 
65–71 1.3 700–870 2.5 700–880 2.9 
TDS (mg/L) CaH (mg/L CaCO3)a Alk (mg/L) CaCO3) 
50–300 0.1 10–11 0.6 10–11 
400–1,000 0.2 12–13 0.7 12–13 1.1 
Temperature (°C) 14–17 0.8 14–17 1.2 
18–22 18–22 18–22 1.3 
23–27 23–27 27–23 1.4 
28–34 1.1 28–35 1.5 
0–1 2.6 35–43 1.2 36–44 1.6 
2–6 2.5 44–55 1.3 45–55 1.7 
7–9 2.4 56–69 1.4 56–69 1.8 
10–13 2.3 70–87 1.5 70–88 1.9 
14–17 2.2 88–110 1.6 89–110 
18–21 2.1 111–138 1.7 111–139 2.1 
22–27 139–174 1.8 140–176 2.2 
28–31 1.9 175–220 1.9 175–220 2.3 
32–37 1.8 230–270 230–270 2.4 
38–43 1.7 280–340 2.1 280–350 2.5 
44–50 1.6 350–430 2.2 360–440 2.6 
51–55 1.5 440–550 2.3 450–550 2.7 
56–64 1.4 560–690 2.4 560–690 2.8 
65–71 1.3 700–870 2.5 700–880 2.9 

aCaH, calcium hardness.

Among direct methods for measuring corrosion and scale-forming potential in water, the marble test, Enslow test, calcium carbonate precipitation potential (CCPP) and corrosion coupons are the most common. Corrosion coupons are simple and effective tools for the estimation of corrosion rates in water supply systems and can provide a visual indication of the type of the system corrosion. The Enslow test is a continuous version of the alkalinity difference (marble tests): water is fed continuously to a levelling bulb or separator funnel partly filled with CaCO3, the effluent is filtered through crushed marble so that the filtrate is assumed to be in equilibrium with CaCO3. The CCPP equals the change in alkalinity (or calcium) values that occurs during passage through the apparatus (Cheng et al. 2010; Kumar et al. 2012; Bernats et al. 2012). The CCPP is an electrochemical method that measures the electric current produced when dissolved oxygen is reduced on a rotating electrode, and the marble test determines scaling potential of water with precipitated or dissolved amount of lime under selected laboratory conditions (Merrill & Sanks 1979; Nawrocki et al. 2010).

Various similar formulas have been used to calculate pHs, some of which presented in Equations (1)–(3).

The general equation is: 
formula
1
In the LS method, pHs is calculated by Equation (2) (De Zuane 1997). 
formula
2
where Ca2+ is calcium hardness (mg/L as CaCO3) and alk is water alkalinity (mg/L as CaCO3).

This calculation is valid, if pHs is more than 9.3.

In the Langelier saturation index, pHs is calculated by Equation (3). 
formula
3
The city of Bandar Abbas is located in southern Iran and is the capital of Hormozgan province. It has a wet and warm climate. The Bandar Abbas water distribution network (BAWDN) consists of over 800 km of pipes made of asbestos-cement, steel and polyethylene materials.

Due to the importance of corrosion and scaling, several experiments have been carried out for BAWDN by the Bandar Abbas water authorities, but various interpretations have been drawn from the results. The differences assessments of water condition could be due to use of different methods (indices), so there is not a clear description of BAWDN corrosion condition; accordingly this study was conducted to find the most appropriate index to BAWDN condition by using direct and indirect methods.

MATERIALS AND METHODS

Evaluation of water corrosivity and scaling properties was based on physicochemical parameters and stability indices. For this purpose, the BAWDN was divided into 15 clusters (Figure 1), based on divisions of the Bandar Abbas water authority. Three 1 litre samples were taken from each cluster; thus a total 45 samples were collected randomly.

Figure 1

Location of water sampling sites in Bandar Abbas.

Figure 1

Location of water sampling sites in Bandar Abbas.

The most current indices LSI, RSI, PSI, LS and AI were evaluated and compared to a direct method, the marble test. The temperature, pH, electrical conductivity (EC), and TDS were determined at the sampling point in the field using an Elmetron CP-501 pH meter and Aqualytic CD24 TDS meter respectively. Analysis for CO3−2, HCO3, hardness and alkalinity was carried out using titration methods and Merck reagents. Sulphate and chloride were measured by using a Hach 2800 spectrophotometer.

To perform the marble test, two biological oxygen demand bottles (with cork stopper) were used; and two plastic tubes were inserted in the stopper, one for air exhaustion and the other for water discharge; 300 ml of sample water was added to each bottle. The alkalinity test was done using the first bottle immediately. To the second bottle, 0.4 g CaCO3 crystals added and the bottle was placed on shaker (20 rpm; 24 h). By comparing the water alkalinity before and after addition of calcium carbonate, scaling potential of the water was determined; If the first reading is less than the second, water is under­saturated, vice-versa water is corrosive and if both alkalinity readings are equal or very near equal, the water is considered stable (Agatemor & Okolo 2008; Peng et al. 2010; Antony et al. 2011).

Statistical analysis of data was performed using SPSS 19 for Windows. Correlation coefficient values +1 or −1 between the variables show that there is strong correlation; a value of 0 values no relationship between them. In general, the tested parameters showing correlation coefficient values higher than 0.7 are considered to be strongly correlated whereas values between 0.5 and 0.7 show moderate correlation (Giridharan et al. 2008). Pearson product moment correlation coefficients and significant levels of data were calculated to define the correlation between each of the tested parameters of water and indices.

RESULTS

Water quality characteristics of the BAWDN and water stability indices calculations of samples and results of the marble test in each cluster are presented in Table 3.

Table 3

Water quality characteristics associated with corrosion and scaling in BAWDN

Cluster Sample no. Temp (°C) EC (μMoh/cm) pH TDS (mg/L) Cl (mg/L as CaCO3 SO4 (mg/L) Alk (mg/L) THa (mg/L) HCO3 (mg/L) CaH (mg/L) CaCO3 (mg/L) 
27.5 845 7.97 465 158.88 136.39 112 142.6 112 65.40 54.54 
26 813 7.92 448 153.07 131.41 149.2 139.2 111.4 63.84 53.10 
27.5 831 8.21 475.5 162.47 139.47 112.4 134.2 112.4 61.55 57.10 
25 1,107.5 7.94 607.5 207.57 178.19 121.2 154.4 112.8 70.82 65.00 
25 1,079 8.05 593.5 202.78 174.08 117.6 158 121.4 72.47 67.50 
25.5 1,104 607.2 207.46 178.10 121.4 149.4 147.2 68.52 70.50 
25.5 1,215 7.63 668.5 228.41 196.08 147.2 176 138 80.72 64.50 
26 1,169 7.87 643 219.70 188.60 149.6 171.8 138 78.80 68.00 
26 1,161 7.86 638.5 218.16 187.28 137.4 167.4 137.4 76.78 63.50 
10 23 1,173 7.97 645.5 220.55 189.34 147 167 157 76.59 73.40 
11 22.5 1,171 7.96 644.5 220.21 189.04 150.4 166.5 160 76.36 76.40 
12 23 1,187 7.65 663 226.53 194.47 150 171 161 78.43 75.30 
13 23.5 1,181.5 7.97 650 222.09 190.66 148 167 158 76.59 77.00 
14 24 1,153 7.77 634.5 216.79 186.11 134.4 168.8 148 77.42 70.10 
15 25 1,063 7.91 588.81 201.18 172.71 137.8 158.18 151.3 72.55 74.60 
16 25.6 1,019.7 7.6 598 204.32 175.40 144.2 159.432 137.6 73.12 61.30 
17 25.7 957 7.8 615.3 210.23 180.48 150.3 160.3 112.8 73.52 59.00 
18 23.3 1,100 7.7 588.7 201.14 172.68 118.9 158 124.3 72.47 60.30 
19 24.1 954.3 8.1 611.3 208.86 179.31 154 147.1 115.6 67.47 67.60 
20 25.1 1,002.3 7.7 654 223.45 191.83 135.3 138.3 127.9 63.43 68.20 
21 22.6 1,161 7.65 600.6 205.21 176.17 128.8 144 155.9 66.05 73.30 
22 22.4 1,173 7.5 498.9 170.46 146.34 119.6 154.6 161.3 70.91 78.55 
23 24.9 1,104 7.8 527.3 180.16 154.67 130.3 160.4 147.2 73.57 71.69 
24 24.2 1,079 608.1 207.77 178.37 127.8 159.7 138 73.25 74.21 
25 24.6 1,000.2 8.04 645 220.38 189.19 148.3 168.1 120.4 77.10 61.63 
26 27.1 960.6 7.65 596.8 203.91 175.05 135.7 138.2 123.9 63.39 63.20 
27 25.6 954.3 7.87 593.1 202.65 173.97 122.2 141.6 135.8 64.94 66.13 
10 28 23 1,215 8.03 644.5 220.21 189.04 114.7 135.5 130.5 62.15 67.55 
28 24.3 899.3 7.45 607.2 207.46 178.10 133.4 154.9 151.3 71.04 73.68 
30 22.7 1,153 7.66 475.1 162.33 139.36 127.4 155.6 155.7 71.37 76.10 
11 31 23 831 8.21 475.5 162.47 139.47 112.4 167 148 76.59 70.08 
32 24.7 998.1 7.94 607.5 207.57 178.19 121.2 139.4 137.7 63.94 67.06 
33 25 1,079 8.05 417.1 142.51 122.34 117.6 171 137.6 78.43 66.10 
12 34 25.5 1,104 554.3 189.39 162.59 121.4 167 114.8 76.59 55.91 
35 25.7 1,235 7.63 668.5 228.41 196.08 147.2 168.8 133.3 77.42 58.92 
36 26 1,229 643 219.70 188.60 130.6 166 115.6 76.14 55.00 
13 37 27.4 1,161 7.65 638.5 218.16 187.28 119.5 157.2 129 72.10 68.82 
38 23.3 1,173 7.5 623.5 213.03 182.88 147 160.3 155.9 73.52 71.92 
39 21.5 1,171 7.96 644.5 220.21 189.04 150.4 158 161.3 72.47 73.55 
14 40 23 1,300 7.45 663 226.53 194.47 152 167.4 134.9 76.78 68.70 
41 23.5 1,181.5 7.97 650 222.09 190.66 148 138.3 124.4 63.43 66.58 
42 24.3 1,253 7.77 604.5 206.54 177.31 122.4 150.3 160 68.93 74.50 
15 43 25 1,063 7.27 588.81 201.18 172.71 137.8 147.1 151.6 67.47 73.83 
44 26 905.2 7.51 581.5 198.68 170.56 159.6 160.5 145.8 73.61 72.50 
45 27.5 1,107.2 7.86 607.2 207.46 178.10 137.4 158.2 128.5 72.56 69.58 
Cluster Sample no. Temp (°C) EC (μMoh/cm) pH TDS (mg/L) Cl (mg/L as CaCO3 SO4 (mg/L) Alk (mg/L) THa (mg/L) HCO3 (mg/L) CaH (mg/L) CaCO3 (mg/L) 
27.5 845 7.97 465 158.88 136.39 112 142.6 112 65.40 54.54 
26 813 7.92 448 153.07 131.41 149.2 139.2 111.4 63.84 53.10 
27.5 831 8.21 475.5 162.47 139.47 112.4 134.2 112.4 61.55 57.10 
25 1,107.5 7.94 607.5 207.57 178.19 121.2 154.4 112.8 70.82 65.00 
25 1,079 8.05 593.5 202.78 174.08 117.6 158 121.4 72.47 67.50 
25.5 1,104 607.2 207.46 178.10 121.4 149.4 147.2 68.52 70.50 
25.5 1,215 7.63 668.5 228.41 196.08 147.2 176 138 80.72 64.50 
26 1,169 7.87 643 219.70 188.60 149.6 171.8 138 78.80 68.00 
26 1,161 7.86 638.5 218.16 187.28 137.4 167.4 137.4 76.78 63.50 
10 23 1,173 7.97 645.5 220.55 189.34 147 167 157 76.59 73.40 
11 22.5 1,171 7.96 644.5 220.21 189.04 150.4 166.5 160 76.36 76.40 
12 23 1,187 7.65 663 226.53 194.47 150 171 161 78.43 75.30 
13 23.5 1,181.5 7.97 650 222.09 190.66 148 167 158 76.59 77.00 
14 24 1,153 7.77 634.5 216.79 186.11 134.4 168.8 148 77.42 70.10 
15 25 1,063 7.91 588.81 201.18 172.71 137.8 158.18 151.3 72.55 74.60 
16 25.6 1,019.7 7.6 598 204.32 175.40 144.2 159.432 137.6 73.12 61.30 
17 25.7 957 7.8 615.3 210.23 180.48 150.3 160.3 112.8 73.52 59.00 
18 23.3 1,100 7.7 588.7 201.14 172.68 118.9 158 124.3 72.47 60.30 
19 24.1 954.3 8.1 611.3 208.86 179.31 154 147.1 115.6 67.47 67.60 
20 25.1 1,002.3 7.7 654 223.45 191.83 135.3 138.3 127.9 63.43 68.20 
21 22.6 1,161 7.65 600.6 205.21 176.17 128.8 144 155.9 66.05 73.30 
22 22.4 1,173 7.5 498.9 170.46 146.34 119.6 154.6 161.3 70.91 78.55 
23 24.9 1,104 7.8 527.3 180.16 154.67 130.3 160.4 147.2 73.57 71.69 
24 24.2 1,079 608.1 207.77 178.37 127.8 159.7 138 73.25 74.21 
25 24.6 1,000.2 8.04 645 220.38 189.19 148.3 168.1 120.4 77.10 61.63 
26 27.1 960.6 7.65 596.8 203.91 175.05 135.7 138.2 123.9 63.39 63.20 
27 25.6 954.3 7.87 593.1 202.65 173.97 122.2 141.6 135.8 64.94 66.13 
10 28 23 1,215 8.03 644.5 220.21 189.04 114.7 135.5 130.5 62.15 67.55 
28 24.3 899.3 7.45 607.2 207.46 178.10 133.4 154.9 151.3 71.04 73.68 
30 22.7 1,153 7.66 475.1 162.33 139.36 127.4 155.6 155.7 71.37 76.10 
11 31 23 831 8.21 475.5 162.47 139.47 112.4 167 148 76.59 70.08 
32 24.7 998.1 7.94 607.5 207.57 178.19 121.2 139.4 137.7 63.94 67.06 
33 25 1,079 8.05 417.1 142.51 122.34 117.6 171 137.6 78.43 66.10 
12 34 25.5 1,104 554.3 189.39 162.59 121.4 167 114.8 76.59 55.91 
35 25.7 1,235 7.63 668.5 228.41 196.08 147.2 168.8 133.3 77.42 58.92 
36 26 1,229 643 219.70 188.60 130.6 166 115.6 76.14 55.00 
13 37 27.4 1,161 7.65 638.5 218.16 187.28 119.5 157.2 129 72.10 68.82 
38 23.3 1,173 7.5 623.5 213.03 182.88 147 160.3 155.9 73.52 71.92 
39 21.5 1,171 7.96 644.5 220.21 189.04 150.4 158 161.3 72.47 73.55 
14 40 23 1,300 7.45 663 226.53 194.47 152 167.4 134.9 76.78 68.70 
41 23.5 1,181.5 7.97 650 222.09 190.66 148 138.3 124.4 63.43 66.58 
42 24.3 1,253 7.77 604.5 206.54 177.31 122.4 150.3 160 68.93 74.50 
15 43 25 1,063 7.27 588.81 201.18 172.71 137.8 147.1 151.6 67.47 73.83 
44 26 905.2 7.51 581.5 198.68 170.56 159.6 160.5 145.8 73.61 72.50 
45 27.5 1,107.2 7.86 607.2 207.46 178.10 137.4 158.2 128.5 72.56 69.58 

aTotal hardness.

In order to better explain the above table, statistical data of measured parameters are presented in Table 4.

Table 4

Statistical parameters for chemical water quality characteristics in BAWDN

 EC (μMoh/cm) pH TDS (mg/L) Cl (mg/L) SO4 (mg/L) Alk (mg/L) TH (mg/L) HCO3 (mg/L) CaH (mg/L) 
Mean 1,083.9 7.8 595.7 203.5 174.7 134.5 156.5 137.4 71.8 
Max 1,244.8 8.1 651.0 222.4 191.0 149.1 171.7 159.3 78.8 
Min 829.7 7.5 462.8 158.1 135.8 117.1 138.7 111.9 63.6 
St. Dev. 108.7 0.1 54.7 18.7 16.0 9.7 9.3 13.0 4.3 
 EC (μMoh/cm) pH TDS (mg/L) Cl (mg/L) SO4 (mg/L) Alk (mg/L) TH (mg/L) HCO3 (mg/L) CaH (mg/L) 
Mean 1,083.9 7.8 595.7 203.5 174.7 134.5 156.5 137.4 71.8 
Max 1,244.8 8.1 651.0 222.4 191.0 149.1 171.7 159.3 78.8 
Min 829.7 7.5 462.8 158.1 135.8 117.1 138.7 111.9 63.6 
St. Dev. 108.7 0.1 54.7 18.7 16.0 9.7 9.3 13.0 4.3 

After evaluating the relevant parameters for corrosion and scaling of water, the five indices were calculated and are presented with the marble test results in Table 5.

Table 5

Results and interpretation of corrosiona of Bandar Abbas drinking water

  Clusters 
Index 10 11 12 13 14 15 
RSI 7.83 7.80 7.88 7.74 7.85 7.97 8.12 8.03 8.01 8.15 7.80 7.92 7.93 8.07 8.22 
SS SS SS SS SS SS SS SS SS SS SS SS SS SS SS 
LSI − 0.02 − 0.02 − 0.26 − 0.04 − 0.15 − 0.1 0.17 − 0.07 0.04 − 0.17 − 0.16 0.15 − 0.17 0.13 − 0.01 
SC SC SC SC SC SC SS SC SS SC SC SS SC SS SC 
PSI 7.27 7.27 7.58 7.65 7.50 7.51 7.39 7.33 7.39 7.29 7.21 7.40 7.54 7.47 7.53 
SS SS SS SS SS SS SS SS SS SS SS SS SS SS SS 
LS 1.76 2.06 2.03 1.76 1.75 2.06 2.01 1.58 2.06 1.70 1.53 2.20 1.84 1.99 1.79 
HC HC HC HC HC HC HC HC HC HC HC HC HC HC HC 
AI  12.26 12.18 12.26 12.25 12.04 12.12 12.07 12.16 11.98 12.33 12.22 12.04 12.06 11.90 
NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA 
Marble test 1.28 3.15 3.6 3.2 2.78 1.95 2.3 2.15 3.6 3.15 2.35 3.05 3.1 3.25 3.3 
SS SS SS SS SS SS SS SS SS SS SS SS SS SS SS 
  Clusters 
Index 10 11 12 13 14 15 
RSI 7.83 7.80 7.88 7.74 7.85 7.97 8.12 8.03 8.01 8.15 7.80 7.92 7.93 8.07 8.22 
SS SS SS SS SS SS SS SS SS SS SS SS SS SS SS 
LSI − 0.02 − 0.02 − 0.26 − 0.04 − 0.15 − 0.1 0.17 − 0.07 0.04 − 0.17 − 0.16 0.15 − 0.17 0.13 − 0.01 
SC SC SC SC SC SC SS SC SS SC SC SS SC SS SC 
PSI 7.27 7.27 7.58 7.65 7.50 7.51 7.39 7.33 7.39 7.29 7.21 7.40 7.54 7.47 7.53 
SS SS SS SS SS SS SS SS SS SS SS SS SS SS SS 
LS 1.76 2.06 2.03 1.76 1.75 2.06 2.01 1.58 2.06 1.70 1.53 2.20 1.84 1.99 1.79 
HC HC HC HC HC HC HC HC HC HC HC HC HC HC HC 
AI  12.26 12.18 12.26 12.25 12.04 12.12 12.07 12.16 11.98 12.33 12.22 12.04 12.06 11.90 
NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA 
Marble test 1.28 3.15 3.6 3.2 2.78 1.95 2.3 2.15 3.6 3.15 2.35 3.05 3.1 3.25 3.3 
SS SS SS SS SS SS SS SS SS SS SS SS SS SS SS 

aHC, highly corrosive; SC, slightly corrosive; C, corrosive; SS, slight tendency to scale forming; NA, non-aggressive.

As one of the objectives of this study was to compare the common indices to the marble test, the Pearson test was used to investigate the correlation between results of different measurements. Pearson correlation coefficients and significance levels between the marble test and indices indicate that there is no significant correlation (Table 6). So, to evaluate the relationship between marble tests and indices, we compared the percentage of samples with corrosive or scale-forming results as determined by indices and marble tests. Based on the results of the RSI, PSI and AI all samples were stable and showed a slight tendency to scaling, while based on the LSI, 73% of samples were slightly corrosive and the rest showed a slight tendency to scaling, according to the LS, all samples were highly corrosive. The marble test results showed that water of all 15 clusters tended to be scale forming.

Table 6

Pearson correlation coefficients and significant levels among indices and marble results

  LSI RSI PSI AI LS Marble 
LSI r  0.963** −0.029 −0.983** −0.181 −0.149 
p  0.000 0.850 0.000 0.234 0.327 
RSI r 0.963**  −0.258 −0.929** −0.184 −0.039 
p 0.000  0.087 0.000 0.226 0.799 
PSI r −0.029 −0.258  0.039 0.187 −0.242 
p 0.850 0.087  0.797 0.219 0.109 
AI r −0.983** −0.929** 0.039  0.208 0.215 
p 0.000 0.000 0.797  0.171 0.157 
LS r −0.181 −0.184 0.187 0.208  −0.164 
p 0.234 0.226 0.219 0.171  0.281 
Marble r −0.149 −0.039 −0.242 0.215 −0.164  
p 0.327 0.799 0.109 0.157 0.281  
  LSI RSI PSI AI LS Marble 
LSI r  0.963** −0.029 −0.983** −0.181 −0.149 
p  0.000 0.850 0.000 0.234 0.327 
RSI r 0.963**  −0.258 −0.929** −0.184 −0.039 
p 0.000  0.087 0.000 0.226 0.799 
PSI r −0.029 −0.258  0.039 0.187 −0.242 
p 0.850 0.087  0.797 0.219 0.109 
AI r −0.983** −0.929** 0.039  0.208 0.215 
p 0.000 0.000 0.797  0.171 0.157 
LS r −0.181 −0.184 0.187 0.208  −0.164 
p 0.234 0.226 0.219 0.171  0.281 
Marble r −0.149 −0.039 −0.242 0.215 −0.164  
p 0.327 0.799 0.109 0.157 0.281  

**Correlation is significant at the 0.01 level (two-tailed).

DISCUSSION

Based on the results of the present study, all measured chemical parameters of water of BAWDN met the required standards. Results showed that the water in Bandar Abbas is mildly hard (average TH = 156.5 ± 9.3 mg/L as CaCO3) with a good buffering capacity, so this water is generally not corrosive, and this condition is as a result of sufficient alkalinity levels (average total alkalinity = 134.5 ± 9.7 mg/L as CaCO3) and suitable pH (average pH = 7.8 ± 0.1). Although high concentrations of SO42– (average = 174.7 ± 16 mg/L) and chloride (average = 203.5± 18.7 mg/L) are present in the water, the influence of hardness and alkalinity was dominant, so that the water has a tendency to scale formation overall.

There were also inequalities among the results of calculated indices and the marble test which may be caused by emphasis of various indices on different parameters of water; for example, the LI provides an indication as to whether a water will precipitate CaCO3 (s) or if it is under-saturated with respect to calcium (Ca2+ (aq)) and bicarbonate (HCO3 (aq)), while the LS emphasises sulphate and chloride concentration.

The recommended value for sulphate and chloride in drinking water is 400 mg/L; the mean values measured for these anions were below the standard, so the two anions cannot be the main reason for water corrosivity.

As a limitation of this study, it should be noted that many factors, such as mineral properties of water, age of water treatment plant structures, dissolved oxygen concentration and environmental temperature, and atmospheric conditions (e.g. precipitation), that could affect the tendency of water to corrosion are not included in the study due to the difficulty of obtaining their values.

The tendency of water to be corrosive or scale forming can be assessed in different ways, but as some direct techniques are costly and time consuming, we are interested in using simpler methods, such as comparative techniques and scaling and corrosion potential indices. Due to the possible different interpretations of various water stability indices, finding the most appropriate index would be helpful in managing water distribution systems to maintain safe drinking water quality.

A study of the potential for scale formation and corrosion of drinking water in south Jordan, showed that based on LSI and RSI values, water samples were slightly corrosive, while based on CCPP values, samples showed no tendency to promote corrosion (Al-Rawajfeha & Al-Shamaileh 2007), thus partially confirming the results of the present study.

Overall, the water of BAWDN is slightly scale forming and among the evaluated indices, the most suitable indices to the BA network condition are AI, PSI and RSI.

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