Here are some numbers from Yomiuri Shinbun article (9/20/2011):
200 to 500 tonnes of groundwater per day to the basements of reactor buildings and turbine buildings of Reactors 1, 2, 3 and 4.
105,000 tonnes of highly contaminated water in the basements at the end of May
90,000 tonnes of this water have been processed by TEPCO up to September 13
102,000 tonnes of highly contaminated water in the basements as of September 13
87,000 tonnes of water added
Of that 87,000 tonnes, estimated 47,000 tonnes were recirculated back into the reactors, leaving 40,000 tonnes of water to have been coming from somewhere.
TEPCO now admits that the rainwater contribution to this amount is only a small portion, and most is from groundwater.
40,000 tonnes divided by 180 days equals is 222 tonnes. Hmmm. Where did that 500 tonnes per day number come from?