**7. Conclusions**

Our results show that drinking water from households, reservoirs, and bottled water was contaminated with heavy metals. The levels of heavy metals obtained were lower than the permissible limits set by the US-EPA, WHO, and BOBS, except for Pb, which has no safety threshold. Lead concentrations were higher than the US-EPA recommendations for households, treated, and untreated water, whereas bottled water contained no Pb. Whilst Pb is present in drinking water because of its dissolution from natural sources, the primary source at the household level is plumbing systems in which the pipes, solder, fittings, or service connections to homes contain lead. PVC pipes, largely used in Botswana, contain lead compounds that can be leached from them and result in high lead concentrations in drinking water. The pH values, temperature, and total dissolved solids (TDS) were all within the recommended limits in this study and, therefore, could not be attributed to the high Pb concentrations.

Whilst the levels of heavy metals were generally low in drinking water in this study, major concerns were observed on the increasing Pb concentrations after treatment and at the household level. Additionally, there is evidence from recent research that low-level mixtures of As + Pb and Cd + Pb can induce synergistic adverse effects [91]. These interactions could negatively affect public health and call for measures to reduce these contaminants.

The variability of heavy metals in drinking water from different locations, particularly Pb could be attributed to a combination of factors including the type of plumbing materials, age of fittings in the building, corrosion of these materials, specific water chemistry, galvanic corrosion between different metals, and the overall condition of the infrastructure. The amount of time the water was standing in the tap before use could have also facilitated Pb leaching. Low water pH can influence the extent of lead and increase corrosiveness; however, in this study, the pH was high enough not to influence piping corrosion. Cd and Pb were not detected in bottled water, suggesting bottled water is a safer drinking water alternative.

The water authorities should aim to reduce Pb in drinking water as it is harmful even if consumed at low concentrations. It is recommended that laws and policies guide industries, manufacturing companies, and other agricultural activities to discard waste accordingly to avoid water contamination. Monitoring the Greater Gaborone sources will also be necessary to ensure they follow lawful standards. The treatment plants should regularly monitor the plumbing materials as they contribute to heavy metals in drinking water through leaching and corrosion. The design of the plumbing system of new buildings should be approved and inspected by the regulatory body. Consumer awareness campaigns on safer plumbing materials and maintenance should be initiated.
