Aim :One of the most important and influential pollutants in the water is heavy metals, which exceeds its permissible levels causing various diseases, including cancer. The aim of this study was to review the relationship between the amount of heavy metals in drinking water and cancer and provide a more effective solution.
 
Methodology:This was a systematic review using the PRISMA protocol to search literatures in international (PubMed, Google Scholar, Science Direct) and national (SID, Magiran, and MedLib) databases. According to the PICOS strategy, all published papers were retrieved in English and Persian languages until February 2020 using different combinations of keywords such as water, heavy metals and cancer and the Persian equivalent keywords. Final selected papers were critically appraised with the PRISMA checklist.
 
Results:Results of review studies showed that the presence of heavy metals in water has many effects on human carcinogenic risk. In some studies, analyzes of water samples have shown a significant relationship between the amount of heavy metals and the incidence of cancer. Calculation of various index such as Carcinogenic Risk (CR), Total Carcinogenic Risk (TCR), Excess Lifetime Cancer Risk (ELCR) index, Health Risk Assessment index (HRA_EPA) on the carcinogenic effects of heavy metals and its comparison with standards in various studies show that most heavy metals, especially Arsenic, lead, cadmium and chromium have a high potential for carcinogenicity in humans through drinking water.
Conclusion:Some studies have emphasized the relationship between amount of heavy metals in water to cancer. Increasing the concentration of heavy metals and their compounds from the maximum acceptable concentration in drinking water has adverse effects on human health and leads to mutagenicity or carcinogenesis. To prevent the harmful effects of heavy metals in water, the first step is to control man-made pollutant sources, and continuous monitoring and pre-treatment treatment becomes more important and necessary.