"The only option will be to drain it into the sea and dilute it," Harada told reporters as the head of the Ministry, one day before Prime Minister Shinzo Abe is scheduled to reform the Cabinet.
Since the accident at the Fukushima Daiichi atomic plant in 2011, the owner of the site, the Tokyo Electric Power Company (Tepco), has accumulated over 1 million tonnes of highly radioactive water, used to refrigerate the damaged reactors.
If the work continues at the current pace, Tepco estimates it will run out of storage space by 2022, forcing the company and government to mull measures in order to tackle the problem, according to Efe news.
Tepco is considering emptying the waste water into the ocean as one of the options, a possibility that is still being debated by a government panel tasked with supervising the demolition of the site but that has already been given the green light by Japan's nuclear regulation authority.
Harada's comment, which he offered as a "personal choice", was the most direct statement made by a Japanese government Minister since the option was sailed some years ago.
The government had withdrawn its initial support for the idea owing to opposition from local fishing associations, which see the method as a threat to their industry.
The contaminated water is subjected to treatment to get rid of radioactive isotopes with the exception of tritium and subsequently stored in tanks.
Tritium is not considered dangerous to human health below certain thresholds that vary between countries and international organizations.
According to Tepco, other nuclear plants in Japan already routinely dispose of this in the sea in small quantities.
Since 2015, Tepco has emptied out hundreds of tonnes of processed water with a volume of tritium of between 330-600 becquerels per litre, under the 1,500-becquerel limit under Japanese law.
( With inputs from IANS )