<p>The presence of lead in freshwater can be a global problem. Lead is a metal with two oxidation states 2+ and 4+, the first value is the former most common under environmental conditions. This element has a strong affinity with elements such as oxygen, nitrogen, sulphur, and carbon, which are present in biomaterials. However, in natural water samples it is possible to find other elements with the same oxidation state that, such as Mg and Ca, which can compete for adsorption sites. Furthermore, the biomaterial can introduce these elements into the samples. This study aims to investigate the impact of water hardness on the adsorption of lead by biomaterials derived from waste fruits, such as orange peel, avocado seeds, and tamarind seeds, in natural freshwater samples. To evaluate the influence of water chemistry on removal efficiency, samples with distinct major ion compositions (particularly water hardness) were collected from different water bodies to conduct lead adsorption experiments. The results show that the presence of Ca²⁺ and Mg²⁺ ions affects the lead adsorption process by biomaterials. Therefore, waste disposal is environmentally friendly. Orange peel is the best option for removing lead and reducing water hardness when samples values are high.</p>