Protecting Limited Water: Saving, Reuse & Rain

Is Japan really a "water-rich country"?

Japan's average annual rainfall is said to be about twice the world average, and the country is blessed with rivers and groundwater, so it is often assumed to be "immune to water shortages." However, looking at water resource data from the Ministry of Land, Infrastructure, Transport and Tourism (MLIT), Japan's per-capita water resources are by no means abundant.

Domestic water use and seasonal imbalance

Japan's annual rainfall varies greatly by region and season, concentrated during the rainy season and typhoon season, while many regions suffer from low rainfall and drought from winter through spring. The terrain is mostly steep mountains with short, fast-flowing rivers, so much of the rain that falls flows out to sea in a short time. Even after drawing water from dams and rivers, a dry rainy season or a year with few typhoons can quickly require drought countermeasures such as water restrictions or reduced-pressure supply. Population concentration in urban areas is another factor making water supply and demand harder to manage: many people depend on the water sources of a limited river basin, so when one water system suffers a drought, the effects tend to spread across a wide range of daily life and industrial activity. As building new dams becomes harder due to land acquisition and environmental concerns, how to use existing water resources without waste, recycle them, and combine diverse water sources has become an important theme of water policy.

Cities like the Fukuoka metropolitan area, which lack a major source river, have repeatedly suffered severe droughts. The "Great Fukuoka Drought" of 1978 involved roughly 287 days of prolonged water restrictions, greatly affecting citizens' lives and economic activity. This experience became the starting point for the desalination facility and water-saving urban development described later in this article.

The indicator called "water resource availability"

It is precisely because of these structural constraints that it becomes important to increase "usable water" through recycling, storage, and securing diverse water sources, rather than using water once and discarding it. The reclaimed wastewater, rainwater harvesting, seawater desalination, and water-saving devices introduced in the following chapters are all initiatives based on this idea.

The challenge of aging water infrastructure

It's not just the "quantity" of water resources that matters — the "quality" of the infrastructure delivering that water is also an issue. Much of Japan's water piping was built during the period of rapid economic growth, and pipes exceeding their statutory service life are increasing nationwide. Aging water pipes carry a high risk of leaks, and treated water can be lost underground before reaching consumers. Protecting limited water resources requires not only securing water sources but also reducing losses in the delivery process. In recent years, sensor technology for early leak detection and AI-based pipe deterioration diagnostics have been introduced, and water utilities across the country have begun narrowing down which sections should be prioritized for renewal within limited budgets.

In regions with declining population, water utility revenue is falling while infrastructure renewal costs remain unchanged, making the business environment for water utilities increasingly difficult. Renewing aging pipes, achieving efficiency through regional consolidation, and utilizing the reclaimed water, rainwater, and water-saving technologies introduced in this article are all mutually complementary efforts to maintain a sustainable water supply system.

"Virtual water": the invisible water import

Virtual water refers to an estimate of the amount of water that would be needed if a country importing food or industrial products had produced those goods domestically instead. According to Japan's Ministry of the Environment, this concept was proposed by Professor Tony Allan of the University of London.

Japan's estimated import volume

According to estimates from 2005, Japan's virtual water imports from abroad reach roughly 64 to 80 billion cubic meters per year, most of it attributable to food. This scale rivals Japan's annual domestic water use. Imports of livestock products and grains such as beef and corn, which require large amounts of water to produce, account for a particularly large share.

Japan's food self-sufficiency rate (calorie-based) has long remained low among developed countries, and the country relies on imports for much of its staple grain, feed grain, and oil-seed needs. Livestock products are especially water-intensive; tracing back to the water used to grow the feed grain that raises the animals, imports of beef, pork, and chicken indirectly consume the farmland and groundwater of their producing countries.

Virtual water hidden in clothing too

Virtual water applies not only to food but also to clothing. Growing cotton requires large amounts of irrigation water, and it is said that growing enough cotton for a single T-shirt can consume several thousand liters of water. According to Japan's Ministry of the Environment, much of the clothing distributed domestically is imported from abroad, meaning the water resources of the producing countries are also behind the clothes we wear.

The origin of the virtual water concept

The concept of virtual water was proposed in the 1990s by Professor Tony Allan, a researcher at the University of London. It is said to have originated while researching why water-scarce regions such as the Middle East manage to avoid severe water shortages — the insight being that by importing grain and food that require large amounts of water, these regions effectively achieve the same result as "importing water." Since then, this idea has spread internationally as an important perspective in discussions of water resource policy and trade policy.

From this perspective, Japan is one of the world's leading "water import powers." While there is little sense of water scarcity domestically, in the countries that produce the food Japan imports, problems such as declining groundwater levels and reduced river flow due to irrigation withdrawal are occurring in some regions. Recognizing that our dinner tables are supported by the water resources of distant countries is the significance of learning about the virtual water concept.

• Clothing imports are also a factor in virtual water consumption (cotton cultivation requires large amounts of water)
• Producing 1kg of beef is said to require several thousand liters of water, including feed grain
• Importing from water-scarce countries also carries the risk of worsening local water shortages

Global water scarcity and Japan's position

Water resource issues are not confined to Japan. The United Nations projects that by 2030, the gap between global freshwater supply and demand could reach 40% of required volume, and more than 2 billion people live in countries facing severe water stress. Water stress levels are reported to be rising not only in North Africa and West Asia but also in Central and South Asia.

What is water stress?

The World Resources Institute (WRI) defines water stress as "the ratio of total water withdrawals to the total available renewable surface and groundwater supply." The higher this ratio, the greater the withdrawal relative to available water resources in a region, indicating a higher risk of drought and water scarcity. Agricultural, industrial, and domestic water use all affect this ratio.

While domestic water stress in Japan cannot be called severe, Japan indirectly imports water resources from water-stressed regions through the virtual water described above. If the countries producing the food and products Japan imports face water shortages, the effects could eventually reach Japan's own food procurement. The world's water problems are not "someone else's problem" for Japan either.

SDG 6: "Clean water and sanitation for all"

UN Sustainable Development Goal 6 calls for ensuring access to safe water and sanitation facilities for all people. Hundreds of millions of people worldwide still lack access to safe drinking water, and water scarcity and pollution are issues directly linked to health, education, and economic activity. Water-saving and reclaimed water initiatives within Japan do not directly support these countries, but they can be positioned as efforts that share the idea of using the earth's limited water resources with care.

The UN has also designated 2018–2028 as the "International Decade for Action: Water for Sustainable Development," calling on countries to promote sustainable water resource management and Integrated Water Resources Management (IWRM). An integrated perspective that balances agricultural, industrial, and domestic water use while distributing limited water — not just building water and sewerage infrastructure — is expected to become increasingly important. Agriculture accounts for a particularly large share of global freshwater withdrawals, and improving irrigation efficiency and developing crop varieties that need less water are also key to solving water resource problems. Water issues are closely tied not only to securing drinking water but to food production as a whole.

Reclaimed wastewater as an option

Reclaimed wastewater refers to a system that treats wastewater generated at sewage plants or inside buildings and reuses it for purposes that don't require the high water quality of drinking water, such as toilet flushing, irrigation, and cleaning. Japan's MLIT positions treated sewage water as "reclaimed water" and promotes its use as part of effective resource and energy utilization.

Where it is used

In large buildings and redevelopment areas in major cities, some buildings have reclaimed water systems that treat wastewater generated inside the building and reuse it as toilet flushing water. This not only reduces use of the main water supply but also helps diversify water sources during droughts.

Its place in sewerage policy

In its "New Sewerage Vision," MLIT presents a direction that reconceives sewage treatment plants as "hubs for resources and energy." Rather than simply treating sewage and being done with it, the idea is to supply treated water as reclaimed water and recover energy from sludge, transforming the entire sewerage system into circular infrastructure. Reclaimed water use is positioned as part of this larger policy.

On the other hand, piping for reclaimed water needs to be built as a separate system from the main water supply, and the cost of new construction is a challenge to widespread adoption. As a result, adoption currently tends to proceed preferentially in newly developed large-scale complexes and redevelopment areas. Retrofitting reclaimed water systems into existing residential areas is technically and financially difficult, so a gradual expansion that makes use of existing infrastructure is considered more realistic.

How it differs from reclaimed water use overseas

Some countries, such as Singapore with its "NEWater," treat sewage to an advanced level and reclaim it even for drinking water. Regions with scarcer water resources tend to actively use reclaimed water as a source of drinking water. Japan, by contrast, is relatively well-endowed with water resources, so reclaimed water use is mostly limited to non-drinking miscellaneous uses such as toilet flushing and irrigation. Depending on future drought frequency and the severity of water supply-demand pressures, the uses of reclaimed water in Japan could expand further.

Turning sewage plants into "resource circulation hubs"

Sewage treatment plants have traditionally been treated as an "endpoint" for cleaning wastewater before discharging it into rivers or the sea. In recent years, however, in addition to reusing treated water, there has been a move to redefine sewage plants as resource circulation hubs — using biogas generated from sewage sludge for power generation, or returning the sludge itself to farmland as fertilizer. Water reuse is positioned as part of this multifunctionalization of sewerage systems, evolving beyond mere water-saving measures into initiatives that contribute to the region's overall resource and energy circulation.

Rainwater harvesting: putting rooftop rain to use

Rainwater harvesting — collecting rain that falls on rooftops in a tank for irrigation, car washing, and toilet flushing during disasters — is a relatively accessible way to use water resources. Roughly 300 local governments across Japan offer subsidy programs for installing rainwater tanks and infiltration systems.

Examples of municipal subsidy programs

• Setagaya Ward: up to ¥35,000 per rainwater tank, with an annual cap of ¥140,000 per applicant
• Yokohama City: operates a rainwater storage tank installation subsidy program
• Osaka Prefecture: rainwater tank installation subsidies in cooperation with municipalities

Rainwater harvesting offers water-saving benefits and also has a "runoff suppression" effect, curbing the sudden inflow of rainwater into sewers and rivers during heavy rain. MLIT also promotes its adoption as an initiative that helps reduce the risk of urban flooding.

Rainwater tanks as disaster preparedness

Rainwater tanks serve not only for everyday water saving but also as a disaster preparedness measure, securing household water during water outages. When an outage occurs due to an earthquake or typhoon, drinking water can be covered by stockpiled bottled water, but water for flushing toilets or cleaning tends to fall unexpectedly short. Rainwater tanks installed outdoors are increasingly recognized as a piece of household disaster-preparedness equipment that secures this kind of "household water."

At a larger scale, some facilities build large-capacity underground storage tanks — bigger than a household rainwater tank — beneath schools and parks, storing rainwater for toilet use during disasters and for irrigation in normal times. From small household rainwater tanks to large public storage facilities, the underlying idea is the same regardless of scale: store the rain where it falls and use it on the spot.

Checkpoints when choosing a rainwater tank

• Capacity: compact tanks of around 100–300 liters are common for detached houses
• Installation location: choose a flat, stable spot near a downspout
• Material and durability: check whether the material can withstand outdoor UV exposure and temperature swings
• Design: slim tanks with concealment covers designed to fit the landscape are becoming more common

When using a subsidy program, the eligible tank capacity and installer conditions vary by municipality, so it's essential to check the latest conditions with your local government office or website before purchasing. Many programs have an annual budget cap, and depending on timing, applications may already be closed for the fiscal year.

Seawater desalination: a lifeline for drought-prone cities

In regions with scarce river water sources, efforts are underway to desalinate seawater and add it to municipal water supplies. A representative example is Fukuoka City's "Mamizu Pia" (the Fukuoka District Waterworks Agency's Uminonakamichi Nata Seawater Desalination Center).

The case of Fukuoka's "Mamizu Pia"

The Fukuoka metropolitan area has no major source river other than the Chikugo River, and has repeatedly suffered drought due to population growth and low rainfall trends. Completed in 2005 at a total project cost of ¥40.8 billion, "Mamizu Pia" is a reverse-osmosis seawater desalination facility with a production capacity of 50,000 tons per day, supplying part of the water delivered by the Fukuoka District Waterworks Agency.

The concentrated brine produced during desalination, with roughly twice the salinity of normal seawater, is not simply discharged into the sea — efforts are also underway to consider its effective use. While seawater desalination is considered energy-intensive, it continues to be examined in various regions as a hedge against drought risk. For more on the reverse osmosis membrane technology, see How Toray's Reverse Osmosis Membranes Are Solving Water Scarcity: The Mechanics of Seawater Desalination.

The 1978 great drought as a turning point

Fukuoka City experienced the "Great Fukuoka Drought" from 1978 into the following year, involving 287 days of prolonged water restrictions. Life continued for months with water flowing only a few hours a day, and water trucks were dispatched more than 13,000 times in total. Learning from this experience, Fukuoka City adopted water-saving urban development as a policy goal, shifting toward risk-diversified water management that combines multiple sources: the spread of water-saving devices, receiving water from the Chikugo River, and the development of the seawater desalination facility.

Costs and challenges of desalination

Seawater desalination provides a stable water source independent of rivers and groundwater, but it consumes large amounts of electricity to force seawater through reverse osmosis membranes, and construction and operating costs tend to be higher than for river-based water sources. As a result, many municipalities position river water as the primary source in normal times, with desalination facilities serving as a backup during droughts or disasters. "Mamizu Pia" is likewise operated to cover part of the Fukuoka metropolitan area's water demand.

What happens to the concentrated brine by-product

When seawater passes through a reverse osmosis membrane to extract fresh water, the remaining salt is discharged as brine at roughly double the concentration. Returning this concentrated brine directly to the sea in large quantities raises concerns about effects on salinity and ecosystems in the surrounding waters, so care is required in discharge methods and dilution. The Fukuoka District Waterworks Agency continually seeks out uses for this concentrated brine, working to treat the by-product as a resource rather than simple waste.

Looking globally, in arid regions with scarce river water sources such as the Middle East and Australia, seawater desalination accounts for the majority of the water supply in some countries and regions. In Japan, the share of seawater desalination remains limited for now, but given that climate change could alter rainfall patterns and change the frequency and scale of droughts, its importance as an option for diversifying water sources may grow.

The evolution of water-saving devices: the most familiar household step

The most familiar step in protecting water resources is water conservation at home. Toilet flush volume in particular has decreased significantly over the past 30 years.

The evolution of water-saving toilets

Major manufacturers such as TOTO and LIXIL have developed technology that improves flushing methods so that even a smaller amount of water can thoroughly flush away waste, dramatically reducing household toilet water use. Simply replacing an old toilet with the latest water-saving model can save several thousand yen a year on water bills. Since the advent of water-saving toilets, it has also become standard to separate levers or buttons for full and half flushes, allowing the minimum necessary amount of water to be used depending on the purpose — another major contribution to reducing household water use.

• When washing dishes, use a basin instead of running water continuously
• Do laundry in full loads to reduce the number of washes
• Switch to a water-saving showerhead
• Turn off the tap frequently while brushing teeth or washing your face

Breakdown of household water use

In a typical household, bathing, toilets, cooking, and laundry account for the main share of water use. Bathing and toilets together are said to account for nearly half of in-home water use, making these two areas especially impactful for water saving. Simply switching to a water-saving showerhead can significantly reduce actual water flow while maintaining the same perceived water volume, and such products are becoming widespread.

Washing machines and dishwashers have also improved in water efficiency year by year, and replacing an old unit with the latest energy- and water-saving model can cut both electricity and water bills simultaneously. Keeping water efficiency in mind when replacing appliances is another way to build sustainable water-saving habits without extra effort.

An era when saving water means "technology," not "endurance"

Water conservation used to rely heavily on "behavioral endurance," such as shortening shower time or not leaving the water running. Today's water-saving toilets and showerheads, however, are designed to save water through technology rather than relying on user endurance — for example, by atomizing water into a fine mist to maintain perceived water volume while reducing actual usage, or using swirling flow to flush waste efficiently with less water. The fact that water resources can now be protected without changing everyday convenience is a major advance in recent water-saving devices.

In apartment buildings and offices, sensor-activated automatic faucets and mechanisms that automatically shut off water after a set time are also spreading, preventing water waste without relying on individual awareness. These hardware-based measures point toward incorporating water conservation into daily life as "a built-in default," rather than as "a special effort."

Corporate efforts to conserve water sources

The movement to protect water resources is spreading not only among government bodies and individual households but also among companies that use groundwater as industrial water. A representative example is Suntory Holdings' "Suntory Natural Water Forests" program.

"Water Positive": nurturing more than double the water pumped, through forests

Suntory scientifically identifies water source recharge areas around its factories and continues efforts to conserve and maintain forests by entering into long-term forest management agreements with local governments and forest owners. As of 2026, the program has expanded to 27 sites across 16 prefectures, covering over 12,000 hectares, and Suntory says it recharges more than double the volume of groundwater that its domestic factories pump — a state it calls "Water Positive."

Forests act as a "green dam," allowing rainwater to infiltrate the soil and gradually accumulate as groundwater over time. Restoring degraded forests and maintaining conditions where rainwater properly soaks into the ground protects not only a factory's water source but also the rivers downstream and the region's overall water cycle. The idea of a company recharging water beyond what it consumes for its own business activities, rather than simply consuming it, represents one culmination of technologies for protecting water resources.

Efforts like this to conserve water sources are spreading beyond beverage makers to manufacturing industries in general that rely heavily on groundwater or river water. Quantifying the impact of business activities on water resources as a "water footprint" and returning more water to the local natural environment than is used is becoming an important indicator in corporate environmental management. Forest maintenance around water source areas is also expected to have secondary benefits, such as local employment and fostering the next generation of forestry workers.

How to combine these water-protecting technologies

Reclaimed wastewater, rainwater harvesting, seawater desalination, and water-saving devices are not standalone measures — they are most effective when combined according to each region's water situation. In cities lacking river water sources, desalination and reclaimed water use are practical options; in residential areas, spreading rainwater tanks and water-saving devices is more realistic.

How climate change affects water resources

Climate change is another factor making water resource management increasingly difficult. Global warming is pointed to as increasing both localized heavy rainfall and prolonged low rainfall or drought, making dam operations and water-use planning based on past experience less reliable. Rain that falls intensely in a short time tends to overwhelm the capacity of rivers and sewers and flow out to sea quickly, while prolonged periods of low rainfall raise drought risk.

Amid these increasingly "extreme" precipitation patterns, rainwater harvesting that stores rain on the spot, reclaimed wastewater that reuses sewage instead of wasting it, and seawater desalination that doesn't depend on rivers, all also serve as adaptation measures against climate change. Rather than relying on a single water source, combining multiple options is a way to prepare for future uncertainty.

Bringing the virtual water perspective into daily life

While there are limits to how much water saving can be achieved at home, reducing food waste and choosing not to buy more food or clothing than necessary also indirectly helps protect overseas water resources. Being conscious of both "visible water" and "invisible water" is the first step toward sustainable water use.

The respective roles of municipalities, companies, and individuals

Efforts to protect water resources consist of three overlapping layers: infrastructure development led by national and local governments, technology development for water-saving devices led by companies, and daily usage habits managed by individuals. Large-scale infrastructure such as reclaimed water systems and desalination plants is led by municipalities and water utilities, but installing a rainwater tank or replacing water-saving devices are things individuals can decide to start today.

SDG 6, "Clean water and sanitation for all," calls not only for building water infrastructure but also for managing water resources sustainably. Because turning on a tap and having water flow instantly has become taken for granted in Japan, there are few opportunities to think about where that water comes from and where it goes after use. Learning about mechanisms such as reclaimed wastewater, rainwater harvesting, and seawater desalination is an opportunity to reconsider this "taken for granted" assumption.

All the technologies and systems introduced in this article are already operating in Japan today. No special expertise is needed to look into a rainwater tank subsidy program, consider switching to a water-saving toilet or showerhead, or make an effort to reduce food waste — anyone can start today. To pass on limited water resources to the next generation, it's worth starting by simply becoming aware, in daily life, of where water comes from and where it goes.