**6.4 Nickel (Ni)**

The amount of Nickel (Ni) in the five (5) different samples at five different points, as shown in **Table 6**, decreases at points 1, 2, 3, and 4, while the amount decreases dramatically at point 5.

The amounts at all points (i.e., points 1–5) were less than 0.0100 mg/L in February and March samples. The mean of the three months is 1.0502, 0.0100, and 0.0100, the standard deviation is 0.5094, 0.0112, and the variance is 0.2595, 0.0001, and 0.0001. The coefficient of correlation between the three (3) months was discovered to be zero (0), indicating that there was no correlation between them. WHO has recommends a nickel concentration of 0.02 mg/L for drinking water.

### **6.5 Zinc (Zn)**

The amount of Zinc (Zn) in the five (5) different samples at five different points in mg/ kg, as presented in **Table 7**, for January samples, decreased at points 1 and 2, but increased at points 3 and 4, and decreased at point 5, while increasing at points 1, 2, 3, and 4.

For February samples, the amount decreases from point 1 to point 2, while the amount decreases from point 3 to point 5, and there is a sudden increase in the amount at point 5 that is greater than the amount at points 1, 2, 3, and 4.

For March samples, the amounts at points 1 and 2 increase, but the amount at point 3 decreases to less than that at points 1 and 2, while at point 4, there was a drastic decrease in the amount compared to that at points 1, 2, and 3, but at point 5, there was

**Figure 1.** *Comparison between mean samples and WHO maximum concentration limit.*

**Figure 2.** *A graph of concentration (mg/L) of heavy metals.*

a drastic increase in the amount that was more than that at points 1, 3, and 4, but less than that at point 2. The mean of the three months is 0.1194, 0.2137, and 0.2596, the standard deviation is 0.0182, 0.0219, and the variance is 0.0003, 0.0005, and 0.0021. The coefficient of correlation between the three (3) months was discovered to be zero (0), indicating that there was no correlation between them.

The heavy metals' mean concentrations (mg/L) (chromium, iron, nickel, and zinc), and a calibration curve (**Figure 1**) was plotted using the table to indicate the heavy metals' concentrations (mg/L) against the metals.

The curve demonstrated an increase in heavy metal concentration (mg/L) in the samples as follows. Iron (Fe) > Zinc (Zn) > Nickel (Ni) > Chromium (Cr). This indicates that iron (Fe) has the highest concentration value in the samples (**Figure 2** and **Table 8**).
