Heavy metal(loid) (HM) contamination in water arises from various anthropogenic activities and natural processes, posing risks to human health through ingestion and dermal absorption. Although numerous studies have assessed health risks associated with HMs in water, inconsistencies in the selection of exposure and toxicity factors limit comparability and reliability across studies. To address this gap, the aim of this review was to provide a comprehensive synthesis of exposure and toxicity factors used in health risk assessment (HRA) of HMs in water. The objectives were to evaluate the variability in ingestion, body weight, exposure duration and frequency, and dermal contact parameters, as well as in reference doses and cancer slope factors and to propose standardized values and statistical distributions for more consistent risk estimation. A systematic search of the Scopus database retrieved 806 studies, from which highly cited articles (≥100 citations) and recent publications (2023–2025) were prioritized for analysis. The findings revealed substantial variability in factors and showed that probabilistic approaches, particularly Monte Carlo simulation, were increasingly applied and provided more reliable estimates than traditional deterministic methods. The highest agreement was observed for exposure frequency for ingestion (365 days/year) and skin surface area (18,000 cm²), each applied in 75.5% of cases. By identifying inconsistencies in current practices and proposing standardized exposure and toxicity values and distributions for water, this review is expected to offer practical recommendations to improve the robustness, reliability, and comparability of HRAs, ultimately informing more effective policy-making and water management practices.