As the cleanup of a triple meltdown following an earthquake and tsunami at the Fukushima nuclear power plant drags into its seventh year, one of the biggest continuing threats is less from airborne radioactivity than it is simple water.

On March 11, 2011, the Fukushima plant was devastated by a tsunami, which over the ensuing days sent three of its six reactors into meltdown, while hydrogen explosions cast radioactive iodine, cesium and other fission by-products into the air. More than 160,000 people were forced to evacuated in the wake of the disaster, which has now become synonymous with Chernobyl.

At the time, officials began pumping millions of liters of water into the destroyed reactors to keep them cool, often dumping it from helicopters and spraying it through water cannons. In the years since, the water inundation has become less dramatic, but in the absence of any other way to keep the molten fuel cool, the flow of water continues to flow through the remains of the reactors at the rate of some 160 tons of water a day.

While much of that water undergoes purification to remove significant amounts of radiation, filters can’t cleanse the water of tritium, a radioactive isotope of hydrogen — a process likened by some scientists to separating water from water.

As a result, water contaminated with tritium is building up and space to store it at the disaster site is running out. Of the 1.13 million-ton water storage capacity that the plant has, some 1.7 million tons have been used up.

Cleanup workers have to build a new steel water tank at the rate of one every four days to contain it all, and space to build more is becoming scarce. According to Japan’s Ministry of Economy, Trade and Industry, the tanks already sprawl over an area that could accommodate 32 football fields. All of the storage, says the government, will run out by 2021.

A clock, found in debris on a beach in Fukushima, stopped at the exact time the March 11, 2011 tsunami hit. Photo: - Credit: Nils Bøhmer/Bellona

This looming crisis has left the Japanese government and Tokyo Electric Power Company, which owns Fukushima,  pondering how to get rid of this water – a decision that is generating anxiety and scare headlines as an expert committee weighs whether or not to release the water into the Pacific Ocean.

Despite the national and worldwide case of nerves such a decision might provoke the Japanese government says it can do it without a threat to the country’s fishing industry. Tritium, after all, is a substance that naturally occurs in rivers and seabeds – even tap water. What’s problematic with the tritium at Fukushima, though, is that its levels in the Fukushima water are 10 times higher than Japanese national standards for dumping it.

Because of that, the government’s expert panel is considering several methods for the water’s disposal, including evaporating it, releasing it into the sea after electrolysis, burying it underground or injecting it deep into the geology.

But as cleanup costs continue to spiral, with some Japanese think tanks speculating the final bill could be as much as $470 billion to $660 billion,  releasing the water into the sea – after diluting it – may turn out to be the cheapest option.

It’s not the first battle against water that the cleanup effort has fought. As recently as two years ago, some 400 tons of ground water flowed into the facility daily. Tokyo Electric Power somewhat stemmed that by building an underground wall of frozen soil to staunch the seepage of radioactive water.

has managed to decrease the inflow by installing a 30-yard-long “ice wall” fence that freezing cold brine is pumped through to freeze the soil around it, reports Wired. The chilled soil is meant to create a barrier to keep additional groundwater from spilling into the radioactive area.

But this year, on the seventh anniversary of the disaster, an expert group commissioned by the Japanese government concluded that the subterranean wall is not entirely effective against the deluge, and that other methods of battling leakage have to be devised.