For many years, mercury has been used worldwide for human activities and now the exposure to this metal, both from natural and artificial sources, increases significantly. The set of environmental consequences resulting from mercury biosphere pollution is an alarm signal to end the irresponsible behavior of industrial civilization with regard to water quality. In fact, the harmfulness of water pollution is directly or indirectly reflected on humans, and it is therefore necessary to know better these dangers, including the effects that even small quantities of chemicals from water sources can have on humans. The key points presented in the following pages of this review are: form of mercury exposure, environmental pollution and the effects of mercury pollution. The results described in this paper indicate that mercury is a global pollutant due to persistence, bioaccumulation and environmental toxicity.