Honestly, not much in the way of alternatives. Tritium is very, very difficult to remove from water. Basically the only option, aside from discharge, is to store it in tanks and wait for enough half lives to elapse that the tritium effectively just decays away on its own. The half life of tritium is just over 12 years, so that’ll still be a while longer, and that gets expensive (in terms of both storage costs and space costs). However, tritium is not particularly dangerous, especially at low concentrations.
As usual with radioactive liquids, dilution is the solution. And Japan has diluted this liquid to 1500Bq/liter, far short of their internal legal limit of 60,000Bq/liter, and even far below the WHO limit of 10,000Bq/liter.