This document discusses human health effects of tritium, a radioactive isotope of hydrogen, in drinking water. It provides background on tritium production in CANDU nuclear reactors and monitoring of tritium levels in drinking water near nuclear plants in Ontario from 2001-2009. The document recommends revising Ontario's drinking water standard for tritium to 20 Bq/L based on assessments of health risks from chronic lifetime exposure and achievability without large costs. It also discusses concepts of radiation dose, natural radioactivity in the body, and implications for radiation protection standards at low doses.