It is said that 20% of the world’s earthquakes with a magnitude of 6.0 or higher occur in the vicinity of Japan.^*1 In addition, amid concerns of a major earthquake occurring directly below the Tokyo metropolitan area, megathrust earthquakes affecting the Tonankai area (off the southeastern coasts of Japan), and other future seismic events, municipalities are required to take various measures to protect lives in the event of a major earthquake. In particular, securing drinking water for emergency use is of utmost importance and must be prioritized above all else. What makes this difficult, however, is coming up with a system for storing large amounts of water in a safe and drinkable condition, and the cost of doing so.

One of the measures being introduced is the earthquake-resistant emergency water storage tank, in which a part of the water supply facility is used as a water storage tank. In this system, large-diameter ductile iron pipes are incorporated into part of the water distribution pipelines to serve as water storage tanks, which are used as water distribution pipelines during normal times. But in the event of a disaster such as an earthquake, the gate valves on both ends of the iron pipes are closed, and the water stored in the pipes can be used as an emergency water source. One of the main features of the system is that it functions as a waterway under normal circumstances, so there is no stagnation of water and clean water can be secured at all times.

In addition, ductile iron pipes are made of cast iron, which is tenacious and resistant to external forces and decay, making them earthquake-proof, durable, watertight, and capable of withstanding major aftershocks. Furthermore, the scale and type of water storage can be selected by changing the length of the pipeline, thus reducing restrictions on the installation location. Since the system utilizes underground pipelines, it is economical to bury the system in schoolyards, parks, plazas, parking lots, under roads and so on, so that the area above ground can be effectively used as a temporary evacuation site or for other purposes. Finally, the system is easy to install and the construction period is relatively short, meaning that municipalities across the country are introducing the system according to their own conditions.

In 2005, Yokohama, a densely populated city in the Tokyo metropolitan area, installed an underground disaster water tank in the Minato Mirai 21 area, among the largest of its kind in Japan.*2 It was capable of securing enough drinking water for approximately 170,000 people for three days in the event of a disaster. Since then, we have received an increasing number of orders from municipalities around the country. In FY2014, Kubota installed earthquake-resistant water storage tanks in 23 locations across Japan, including Gonohe Town in Aomori Prefecture, Shiogama City in Miyagi Prefecture, and Kagamiishi Town in Fukushima Prefecture, all of which were affected by the Great East Japan Earthquake. Kubota will continue to pursue the possibilities of ductile iron pipes, including earthquake-resistant emergency water storage tanks, and contribute to the development of cities where water infrastructure can be maintained even in times of disaster.