**6.4 Analysis of the heavy metal pollution index**

To determine the suitability of the drinking water, the heavy metal average concentration of outdoor and indoor tap water data obtained in **Table 3** were used to calculate the HPI index using Eq. (1) and (2). The WHO and BOBS standards were used to determine the appropriate HPI (**Tables 5** and **6**).

It is observed that the drinking water from the water distribution system has a heavy metal pollution index (HPI) of 0.74 (**Table 5**) according to the BOBS standards and 33.18 according to the WHO standards (**Table 6**). Therefore, the HPI of 0.74 indicates that the level of heavy metal pollution in the drinking water, as per the standards set by the Botswana Bureau of Standards (BOBS), is relatively low. BOBS might have established specific limits for heavy metal concentrations in drinking water. With an HPI of 0.74, the water appears to be within the acceptable range according to these


#### **Table 5.**

*Heavy metal pollution index (HPI) of drinking water from water distribution system (BOBS standards).*


#### **Table 6.**

*Heavy metal pollution index (HPI) of drinking water from water distribution system (WHO Standards).*

standards. However, the HPI of 33, as per the World Health Organization (WHO) standards, suggests a higher level of heavy metal pollution index. WHO has more stringent limits for heavy metal concentrations in drinking water, and the water in question seems to exceed these limits.
