The need for high quality water to sustain different ecosystems is an important issue and there is a need for preservation of these natural ecosystems for better access of future generations. Selenium is one of the chemicals which is distributed widely in nature and is found in most rocks and soils at concentrations. It also transported via different ways such as water system of farming, coal burning, silver, gold, coal and phosphate mining, metal purifying, and city landfills. This book provides in-depth technical knowledge on the selenium contamination in water. It starts with a presentation of selenium science, dissemination and health dangers due to this chemical. It has 10 chapters about water quality and its indicators, a background history of selenium, its chemistry and toxicology, its contamination issues, and selenium health benefit as well its hazardous for the human beings. It also explains how to remove selenium from water, and what are the future directions in selenium removal technologies.