another bbc article: http://www.bbc.co.uk/news/world-asia-23764382
From that I think this is a one off discovery of 300 tonnes of highly radioactive water leaking, and in general 300 tonnes of 'not as radioactive' per day leak from the radioactive buildings.
"around 300 tonnes of highly radioactive water had leaked from a storage tank on the site."
Ok, 300 tonnes, but during which time period? Between 2011 and now? And how radioactive? What elements and how much does it contain?