One of the most common received truths about Japan is that it lacks natural resources, which is why it relies so much on imports. Lack of resources was one of the reasons Japan invaded Asia in the last century. But there is one resource that is plentiful, and which is becoming scarce in other regions: water.
In fact, there has been talk that Japan could export fresh water as a form of "security." Japan currently buys a lot of coal from Australia, which is delivered by ship. Those vessels return to Australia empty, and usually have to fill up with sea water for ballast, a risky solution since the water could contain living things that might upset marine ecology systems back in Australia. But the ships could also fill up with fresh water — not necessarily drinking water, but water that could be used in the mining of the coal being sent to Japan. Coal mining requires a lot of water, and Australia doesn't always have enough.
It's estimated that 900 million people in the world do not have ready access to safe drinking water, so Japan should count itself lucky. However, in recent years water supply agencies nationwide have been raising fees or proposing to raise fees on tap water.