**6.3 Heavy metal concentrations**

To the best of our knowledge, this is the first study to assess the HM concentrations (in particular the CALM cations) in drinking water in Botswana. For instance, Smith and others (1994) conducted a water quality study in Gantsi Township, Botswana, but overlooked to evaluate the occurrence of Cd, As, Pb, and Hg in drinking water [72]. The same concern is corroborated by the Botswana Water Statistics Report (2009), which observed that none of the water authorities in Botswana have tested or reported concentrations of CALM [17]. This is despite the national regulations governing drinking water quality specifications enforced by the BOBS [63]. It is, therefore, a pressing need to establish the concentrations of CALM in drinking water in Botswana.

The results obtained in the present study generally complied with the heavy metal (HM) standards set by WHO and BOBS [2, 63]. However, Pb concentrations exceeded the permissible limit set by US-EPA. Generally, the average concentrations showed the order of abundance as Pb > Hg > As>Cd. Furthermore, it was observed that raw water samples measured concentration levels lower than the after-treatment samples except for arsenic (As). In addition, the results showed an upward offset of ~93% in the concentration levels of lead (Pb), particularly in treated water (i.e., indoor household water) compared to untreated water (i.e., raw water) (**Table 2**), partially indicating a possibility of an input source after treatment. This could be ascribed to the residual leaching of HMs (especially lead) from household-level piping and plumbing.

**Table 2** shows that while Cd was not detected in raw water, it was detected after water treatment, in outdoor household taps (representing input from the distribution line), and in indoor household taps. The concentrations were in the order of raw water < after treatment < distribution < households. The mean concentration of Cd in all the locations was less than the permissible limit set by US-EPA, WHO, and BOBS, with the overall mean (±SD) of 0.005 (±0.02) μg/L and 0.003 (±0.01) μg/L for indoor and outdoor concentration, respectively. The slightly higher concentrations


#### **Table 2.**

*Mean (±Standard Deviation) in μg/L of heavy metals in bottled, reservoirs, and households.*
