“When rainwater flows into the sewers, it turns into a flood. If you collect it, it becomes a resource.” This is the view of Makoto Murase – Japan’s rainwater collection pioneer.

For Makoto Murase, rainwater is a tremendous resource – and given the global scarcity we can’t afford to waste it.

In Tokyo in June the hot and humid Japanese summer emerges with the “tsuyu” – the first rainy season, which lasts about six weeks. The autumn rain (“akisame”), falling in September and October, marks the second rainy season. Between July and October and sometimes earlier, Tokyo – like the rest of Japan – is often hit by typhoons, which bring their share of rainfall and storms.

The problem is that the Japanese megalopolis is a densely packed and complex concrete jungle that isn’t always able to handle these heavy rains. Concrete is waterproof, which stops water being absorbed by the soil. Municipal sewers quickly overflow, causing heavy flooding. Tokyo city therefore needed a solution. And it was Makoto Murase who found it the early 1980s.

Makoto Murase was then employed in the wastewater department of the district of Sumida-ku, northeast of Tokyo. With the help of his team, he designed a system that collects rainwater from roofs, filters it through ingenious systems placed in the gutters, and then stores it in large underground tanks. At this point, it is not drinkable but can be used to water green spaces, flush toilets, run washing machines, and extinguish fires. Although Makoto Murase is not the only one who has thought of a rainwater collection system, he was the first to design it on an urban scale.

Meanwhile, Sumida-ku was preparing to become home to largest sumo stadium in Tokyo, the famous Ryōgoku Kokugikan. Makoto Murase saw the perfect opportunity to test his idea. After a first refusal from his bosses, he managed to convince Japan’s conservative Sumo Wrestling Federation of the project’s economic viability. The project proved to be such a success that it profoundly changed the way urban planners, engineers and architects design buildings.

The system invented by Makoto Murase, now nicknamed “Dr. Skywater”, has many advantages: it limits the impact of floods, it achieves significant water and energy savings, it offers the municipality a widely available and “green” reserve of water that it can use in a multitude of ways, and finally, it helps to change perceptions about rainwater. Makoto Murase views this “sky water” as a tremendous resource – and given the global scarcity we can’t afford to waste it.

With this conviction, Makoto Murase now travels Japan – and the world – taking his model to other cities, such as Bangladesh where he participated in the Amamizu project. In 1995, Sumida-ku, followed by Tokyo, made it obligatory to construct underground rainwater tanks for every new building.

The author of several publications, including the Rain Encyclopedia, Makoto Murase is now head of an organization that promotes relatively simple and inexpensive sustainable technology which according to him, could help to solve the water crisis.

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