Japan's crippled Fukushima nuclear plant on Sunday restarted its trouble-plagued water decontamination system for the first time in three months, the utility said.

Tokyo Electric Power Co. (TEPCO) has been forced to repeatedly switch off its Advanced Liquid Processing System (ALPS), which purifies radiation-tainted water, due to a series of glitches plaguing the system since trial operations began last year.

The system has three lines via which it cleans water used to cool reactors at the Fukushima Daiichi plant, where Japan's devastating 2011 quake-tsunami disaster caused a nuclear meltdown.

All three lines are operating together for the first time since mid-March, a TEPCO spokesman said Sunday, after the utility switched one line that had been in standby since May back on.

However the system was still undergoing test runs, and it was unclear when the trial stage would end, he said.

TEPCO is struggling to handle the huge -- and growing -- volume of contaminated water at Fukushima, the site of the worst atomic crisis in a generation.

Thousands of gallons of contaminated water are being stored on site, with no permanent solution for safely disposing of it.