Tritium is a radioactive form, or “isotope", of hydrogen. Like all radioactive isotopes, tritium decays. As it decays it gives off beta radiation.
One of the more common uses of tritium involves glow-in-the-dark lighting and signs. Tritium gas is combined with phosphor to create luminescence. The light source does not require electricity or electrical wiring, making it ideal for exit signs, emergency lighting in commercial buildings and airplanes and for airport runway lights. Tritium is also used as a tracer in biomedical and academic research.
To learn more about tritium in drinking water and the health effects in the body: