1) Tritium readily forms water when exposed to oxygen.
2) As it undergoes radioactive decay, tritium emits a very low energy beta particle and transforms to stable, nonradioactive helium.
3) In a controlled environment, it can have a half life of 12+ years. In the open air or seawater would decay(oxidize) almost instantly.
Here’s the link. Sounds like there must be more than one isotope of Tritium in play because this is the statement saying they can’t remove it from water:
From wiki (it is hazardous if ingested in water)
Tritium is potentially dangerous if inhaled or ingested. It can combine with oxygen to form tritiated water molecules, and those can be absorbed through pores in the skin.
Since tritium is a low energy beta emitter, it is not dangerous externally (its beta particles are unable to penetrate the skin), but it is a radiation hazard when inhaled, ingested via food or water, or absorbed through the skin.[16][17][18][19] HTO has a short biological half-life in the human body of 7 to 14 days, which both reduces the total effects of single-incident ingestion and precludes long-term bioaccumulation of HTO from the environment.[18][20] Biological half life of tritiated water in human body, which is a measure of body water turn over, varies with season. Studies on biological half life of occupational radiation workers for free water tritium in the coastal region of Karnataka, India show that the biological half life in winter season is twice that of the summer season.[21]
According to the U.S. EPA “A recently documented source of tritium in the environment is tritium exit signs that have been illegally disposed of in municipal landfills. Water, which seeps through the landfill, is contaminated with tritium from broken signs and can pass into water ways, carrying the tritium with it.”[22]