Japan’s chipmaking rush pressures Kumamoto’s special water supply

Kimio Katsuya gazes over sprawling, freshly harvested rice fields in Kumamoto Prefecture that will soon be transformed.
“Soon, the paddies will all be filled with water,” Katsuya says on this late October day, sounding wistful. “In the winter, they will look really amazing, with water reflecting the sky and turning blue.”
The serene beauty of expansive paddy fields glistering under the sun is not just an eye-pleaser. It is a symbol of a long-running community-wide effort to preserve the prefecture’s groundwater, which is relied upon by at least 1 million people as well as countless businesses.
But the arrival of Taiwan Semiconductor Manufacturing Co. in Kumamoto — drawn by the national government’s all-out efforts to revitalize Japan’s chipmaking industry — threatens to overuse this precious resource, given the massive amounts of water the sector requires.
Aware of the issue, TSMC, its business partners and local governments and civil society groups are hoping that careful measurement, support for existing projects and proper wastewater management can avoid undermining efforts that have been lauded by the United Nations.
Every year from November until March, joint public-private sector groups, including the Kumamoto Groundwater Foundation, at which Katsuya serves as secretary-general, fill post-harvest rice paddies with spring water in an attempt to replenish the groundwater basin and prevent the further lowering of water tables that have long been strained by industry and urbanization.
The groundwater recharge program, which started in various Kumamoto communities decades ago and expanded with the foundation’s establishment in 2012, has worked so far.

In the year from April 2023, for example, with the cooperation of local farmers, a total of 50 hectares of rice paddies were filled with water during the five winter months as part of the foundation’s work, contributing to an estimated groundwater recharge of 4.3 million cubic meters in an underground aquifer — enough clean and mineral-rich water for the region and preventing the aquifer from drying up, the foundation says.
The prefecture’s groundwater is virtually the only source of drinking and household-use water for 1 million residents in 11 municipalities, including the city of Kumamoto, and it is also used by agriculture and industry.
In fact, the city of Kumamoto, with a population of 740,000, is the only city in Japan with a population greater than 500,000 that supplies its citizens with tap water sourced entirely from groundwater, according to the city government.
The abundance of groundwater is due in large part to ground layers formed by the pyroclastic flows from four major eruptions of Mount Aso between 90,000 and 270,000 years ago. These layers, which are extremely porous, lie on top of the bedrock, making it easy for rainwater to permeate them.
“The layers formed by pyroclastic flows are estimated to be as thick as 100 meters, and they work like sponges,” Katsuya says.
The 16th-century feudal lord Kato Kiyomasa, revered locally as “the deity of public works and irrigation,” built weirs and irrigation canals and developed large swaths of land for rice farming. The rice paddies developed by Kato in the middle sections of the Shirakawa river, which remain today, are five to 10 times more likely to absorb rainwater than normal soil, making Kumamoto’s groundwater resources even more bountiful, according to the city government.

Following the postwar industrial development and urbanization of the city, which lowered the water table and worsened water quality, groundwater conservation projects started in the 1970s.
In cooperation with municipalities and businesses across Kumamoto Prefecture, the foundation has also implemented water-saving initiatives, a rice paddy ownership program and “water offsetting,” where individual and corporate groundwater users are encouraged to buy rice and vegetables grown in water recharge areas so farmlands will be maintained.
According to the foundation, water flooding a 100-square-meter rice paddy for four months helps add 600 cubic meters of groundwater, equivalent to the volume of water in a typical 25-meter swimming pool.
These projects have been highly praised both at home and abroad, with the city of Kumamoto receiving the “Water for Life” best practices award from the U.N. in 2013.
There’s no guarantee Kumamoto’s water development will remain sustainable, given a recent surge in demand with the expansion of semiconductor-related companies into the prefecture. The semiconductor industry uses massive amounts of water, especially during the wafer-cleaning process.
Japan Advanced Semiconductor Manufacturing, a joint venture between TSMC, Sony Semiconductor Solutions, Toyota Motors and Toyota-affiliated car parts maker Denso, held the grand opening of its first factory, located in the town of Kikuyo, in February. It will become fully operational by the end of this year.

JASM, whose first plant is expected to use 3.1 million tons of water per year, will soon begin building an even bigger second factory nearby and has told the Kumamoto Prefectural Government that it wants to use a total of 8 million tons at its two plants. Meanwhile, combined with efforts by another local group working on paddy flooding, the total amount of water being artificially recharged in Kumamoto’s rice paddies currently stands at about 20 million tons per year, according to Katsuya.
Moreover, dozens of suppliers and other related firms are expected to move their bases to Kumamoto. The prefecture could get an economic boost from semiconductor-related businesses totaling ¥6.9 trillion ($44 billion) over 10 years, according to a 2023 estimate released by the Kyushu Financial Group.
The location of TSMC’s third Japan plant, also known as a fab, has not been decided. In August, Kumamoto Gov. Takashi Kumamoto flew to Taiwan to make a direct pitch to the company’s executives, asking the semiconductor giant to build JASM’s third factory in the prefecture.
The major investment is adding a layer of uncertainty over the future of Kumamoto’s groundwater.
“After years of work, we have just started to restore the balance between demand and supply of groundwater,” Katsuya says.
“With the expansion of JASM and other firms, we need to step up our recharge effort. But by just how much more, we can’t predict at this point.”
JASM, fully aware of its environmental impact on the local community, has taken a series of preventive steps.
In May 2023, it reached a comprehensive agreement with a local farmers group, the Kumamoto Prefectural Government, Kikuyo and the Kumamoto Groundwater Foundation to work together so JASM can recharge 100% of the groundwater it uses. JASM is helping to expand the water recharge by subsidizing rice farmers who participate in the recharge project and using rice harvested in the paddies in its cafeteria at the plant.

However, Katsuya says there are challenges when it comes to convincing more farmers to cooperate. A few years ago, the foundation met with local farmers to ask them to recharge their paddies with water in the winter, but only 20% of the farmers who showed up at the meeting agreed, he says.
“Many farmers are aging. Some say just continuing with farming in the summer is demanding enough and that they don’t want to tax themselves further,” he says.
Recent government incentives for domestic farmers to grow wheat in response to the Ukraine war and to grow corn to counter soaring feed import prices have added to the challenges of maintaining rice paddies for groundwater, Katsuya says.
At the same time, people in Kumamoto are particularly sensitive about the sector’s impact on water quality. For many, the memory of Minamata disease — severe mercury poisoning caused by chemical factory wastewater during Japan’s rapid postwar economic growth — remains fresh, as it was first discovered in the prefecture.
JASM, which aims to produce 100,000 wafers per month at the two plants, says it is also making sure to properly manage wastewater.
The wastewater from the first plant is separated into 36 categories, with plans to recycle 75% of it, according to the company. Before the wastewater is released to a local public sewage treatment plant, it is treated to lower the levels of pollutants to half the legal limit, JASM says, noting that its real-time water monitoring system automatically reprocesses wastewater that does not meet the standards.

In October, TSMC and JASM also announced a three-year joint research project on Kumamoto’s groundwater with scientists at Kumamoto University and the Prefectural University of Kumamoto.
Takahiro Hosono, professor of earth environmental science at Kumamoto University, is one of the scientists involved. For years, he has worked to build a sophisticated simulation model for Kumamoto’s groundwater system.
With the TSMC-JASM funding, the sum of which has not been disclosed, he hopes to get a more refined picture of what is happening underground. He currently uses groundwater depth and water quality data obtained through a network of observational wells managed by various government bodies and others across the prefecture.
One thing he hopes to study in the future is the condition of groundwater more than 200 meters below the surface, which observational wells don’t provide data for because none are that deep, he says.
“By incorporating other kinds of data, such as that taken from boring surveys for hot springs, and analyzing their water quality, I would like to get a realistic picture of what is happening deep underground.”
Though his work is not directly related to the environmental impact of JASM operations per se, it would eventually help explain the potential impact of a third JASM plant on the Kumamoto groundwater system, if it were to be located in the prefecture, he says.

Fumi Sugita, professor of hydrology at the Chiba University of Commerce, who is not involved in Kumamoto groundwater research, says Kumamoto is one of the very few cities in Japan where extensive observational underground data is available.
Two giant jolts that hit the prefecture in April 2016, which damaged numerous structures including the iconic Kumamoto Castle, also affected groundwater conditions. A pond in Suizenji Park, a popular Japanese garden in the city of Kumamoto, temporarily dried up immediately after the quake, while groundwater levels rose by 10 meters in other areas. Such phenomena were closely studied and reported, further advancing research into this field, Sugita says.
To cope with the rising demand for water, however, long-term monitoring of groundwater quantity and quality is crucial, Sugita says, pointing to the limits of natural resources.
“The current initiatives don’t mean groundwater can be used limitlessly,” she says. “The third-party surveillance of wastewater being released into the environment, by the prefectural government and residents, will play a key role in preserving the quality of Kumamoto’s water.”