The Sueddeutsche Zeitung is rather "liberal" than "left", it just does not equal your point of view, and from this point everything must be politically 'left'
It is not only Tritium though, and what exactly is being done with the filters after the water has been "cleaned"?
As your link provided: 30 percent of the water is being "cleaned, that leaves 70 percent i guess. And the whole water cooling system has cracks everywhere, so water flows through the ruins, all the time since 2011, and is being exchanged with sea water.
As they just found out the central off limits section is still too "hot" to come near it, except for robots.