Water leaks Tokyo subway?

Noticed several times in the subway system the cieling being covered in plastic and sometimes water running by the stairs. In Bakurocho station was water running from several parts of the wall near the train track.

How come?

How come? Because it's underground. It's called "groundwater". Of course, it's not supposed to be leaking, and it certainly doesn't look good. Meanwhile, there are people taking photographs of it.

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