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A World-class Pure Groundwater City Kumamoto, Japan

最終更新日:2015年3月16日
環境局 環境推進部 水保全課TEL:096-328-2436096-328-2436 FAX:096-359-9945 メール mizuhozen@city.kumamoto.lg.jp
Kumamoto region

 The drinking waterserving Kumamoto City's population of about 740,000 is provided by groundwater. In fact, it is the only city in Japan of over 500,000 people which can make such a claim. This fact is the only one in Japan among the cities with a population of over 500,000 and actually very rare in the world also.
 The land area of the Kumamoto region is about 1,041 km², and continues from the outer rim of Mt. Aso, where there are 11 municipalities, including Kumamoto City, whose total population is more than one million. Groundwater provides most of the drinking water for this entire region.
 Therefore, it is essential for us to maintain and hand down this precious groundwater resource to our descendants. So we, all the municipalities, are collaborating to conserve groundwater. This effort has received high praise internationally, and Kumamoto City received the "2013 U.N. Water for Life" Best Practice award.

 
Hydrological Cycle System of the Kumamoto Region

 The hydrological cycle of the Kumamoto region is unique. Annual precipitation here is about 2,000 mm. The volume of rain is 2.04 billion m³, and one-third evaporates, another one-third flows into the rivers, and the rest, which is about 0.6 billion m³, becomes groundwater. The fact that Kumamoto City has never experienced a suspension of water supply - even at a time of drought - is the result of this hydrologic system.
 The volcano Mount Aso had four huge pyroclastic flow eruptions from about 270,000 years ago to about 90,000 years ago. Those pyroclastic flows were deposited thickly and made soil which easily retains water.
 Then, approximately 420 years ago, the local lord of Higo, Kiyomasa Kato, built many sluices and irrigation channels in the middle basin of the Shirakawa River and developed paddy fields. Water permeates five to ten times more than normal in paddy fields in the middle basin of the Shirakawa river (Ozu-machi and Kikuyo-machi). Since Kiyomasa developed paddy fields where the land had superior water permeability, the result was a huge amount of water reaching underground aquifers.

 
Figure of groundwater system

Figure of groundwater system

 
The Miracle of Water Created by Aso and the Efforts of Our Predecessors
 
The middle basin of the Shirakawa River

The “natural system” of magnificent Aso and the “system of human activity” by Kiyomasa Kato and our predecessors exquisitely combined to produce the groundwater system of Kumamoto. This means the hydrological cycle system in the Kumamoto region was completed about 420 years ago.
 Groundwater flows from the outer rim of Aso to Kumamoto City, taking about 20 years. During this period, minerals and carbonic acid are dissolved into the groundwater in a suitable balance. The result is natural water which is tasty and good for the human body.
 The hydrologic cycle system is a natural manufacturing machine for mineral water and, if we sustain this system appropriately, we can be blessed with wonderful groundwater into the foreseeable future.

 
Flow of groundwater
Flow of groundwater
 
Tap Water of Kumamoto City
 
Water pipe construction in Tatsutayama in the beginningNo. 5 well of the Kengun water source

left: Water pipe construction in Tatsutayama in the beginning
right: No. 5 well of the Kengun water source

Mineral water flows from the tap
 In Kumamoto City tap water for about 740, 000 citizens is provided by groundwater.
From 113 wells in the city, a daily average of 220,000 m³ of water is supplied to the whole city (as of March 31, 2014). There are neither dams nor water purification plants in Kumamoto City as in other cities. Clear groundwater drawn up from wells is treated with the minimum amount of chlorine provided by laws and accumulates in the distributing reservoir or regulating reservoir. Then it is supplied to each household.
 The water works of Kumamoto City were proposed by the city’s third mayor, Karashima, and were started after many complications on November 27, 1924 during the administration of the 7th Mayor Takahashi. At that time, Hakenomiya was a water source and Tatsutayama was the distributing reservoir. The Hakenomiya water source, with its 90 some years of history, was selected as one of 100 modern waterworks of Japan. The water work memorial hall (original pump room), which reflects what it looked like at the beginning, is a government-designated tangible cultural property.
 The Kengun water source is the largest in Kumamoto City. Out of 11 wells, seven are flowing and, among them, the No. 5 well has a daily capacity of water intake of 15,000 m³, so that this well can by itself supply water to more than 60,000 citizens.
※Daily household water consumption per person 227 liters in FY 2013

 
Safe, secure, and tasty tap water
 
Comparison table

 Tap water in Kumamoto City contains a good balance of minerals such as calcium, potassium, which contributes to its health-giving properties and flavor. Furthermore, it is rich in silicon, which is known to contribute to flexibility of blood vessels. It is tap water, but it is actually natural mineral water.
 Minerals in the tap water of Kumamoto City and marketed bottle water are shown in the graph on the left. From this graph, the fact that the tap water of Kumamoto is in fact excellent mineral water is proven.
 Among mineral water bottled in foreign countries, there are some that have very high mineral content. However, they are not so flavorful, and are merely luxury grocery items consumed with a certain purpose. The mineral content of some commercial bottled water is only one-tenth that of Kumamoto’s water.
 Tap water in Kumamoto City is natural mineral water which is tasty and gentle to the body.

 Wells, distributing reservoirs, and regulating reservoirs scattered around the city are connected with pipes whose total length is about the same as the length of the Japanese archipelago (3,310 km as of March 31, 2014). These pipes are monitored and controlled 24 hours at the Water Supply Management Center in the Waterworks Bureau.
 The Waterworks Bureau carries out 91 (as of April 1, 2014) strict water quality inspections for wells and all through to taps every year in order to supply safe tap water to each household.

 
Water quality inspection 1Water quality inspection 2
 
Tap GLP certification
 
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