Properties of water water isotopes. Naturally occurring water is almost completely composed of the neutron-less hydrogen isotope protium. Only 155 ppm include deuterium ( or D), a hydrogen isotope with one neutron, and fewer than 20 parts per quintillion include tritium ( or T), which has two neutrons. Oxygen also has three stable isotopes, with present in 99.76%, in 0.04%, and in 0.2% of water molecules. Deuterium oxide, , is also known as heavy water because of its higher density. It is used in nuclear reactors as a neutron moderator. Tritium is radioactive, decaying with a half-life of 4500 days; exists in nature
Radioactive contamination from the Rocky Flats Plant caused by normal operations rather than accidental releases. From September 1947 to April 1969 there were 5 or more accidental surface water releases of tritium. Tritium, a radioactive element which was found in scrap material from Rocky Flats, was therefore directed in to the Great Western Reservoir. This was uncovered in 1973 and following this, urine samples were taken from people living or working near Broomfield who could have drunk water from the reservoir. The findings of the samples showed that those who were exposed to contaminated water had tritium concentrations near seven times higher than normal (4,300 picocuries per