Say Goodbye to Water Pipes: Japan Built a Home Machine That Purifies and Reuses Almost All Household Water

In January 2026, households in several Japanese municipalities began testing a water system that connects to no municipal pipe. The units, installed next to washing machines, filter and recirculate wastewater from showers, sinks, and laundry, operating independently of the public grid.

The devices are manufactured by WOTA Corp. , a Tokyo-based startup. Field trials started this year in Akita and Ishikawa Prefectures, regions where depopulation has made maintenance of aging water infrastructure financially unsustainable. Local governments are evaluating the systems as a permanent replacement for centralized service.

The WOTA BOX treats greywater using filtration membranes and chemical disinfection, then returns it for domestic use. According to company data, the system purifies up to 97 percent of household wastewater and meets all 51 Japanese tap water quality standards as well as World Health Organization benchmarks for safe reuse. Any water loss is replenished with filtered rainwater.

The Pipes No One Can Afford to Replace

Japan’s Cabinet formalized support for this approach in June 2025. The Basic Policy on Economic and Fiscal Management and Reform 2025 , adopted that month, explicitly calls for “early practical implementation of decentralized water and sewerage systems.” The policy followed years of reporting by the Ministry of Land, Infrastructure, Transport and Tourism on the rising costs of maintaining centralized networks.

Replacing a single kilometer of water pipe costs between 100 million and 200 million yen, depending on location and materials. Between fiscal 2020 and 2024, the national average replacement cost rose by about 20 percent, the ministry reported in March 2025. In Osaka, actual expenditures in some cases reached twice the initial budget.

A 2024 survey by the Ministry of Internal Affairs and Communications found that 60 percent of municipalities had postponed earthquake-resilience upgrades to water infrastructure due to lack of funding. In depopulated areas, some local authorities have begun scaling back services.

How to Fund a Future Without Water Bills

In July 2025, WOTA established the Water 2040 Fund, a 10 billion yen program to support municipalities in adopting decentralized systems. The fund provides financing, planning tools, feasibility simulations, and operational frameworks. Applications opened nationally in mid-2025 and are accepted on a first-come basis.

The company’s implementation model includes digital tools that simulate deployment impact across a 500-meter mesh of municipal areas, identifying priority zones and providing infrastructure planning tailored to local conditions. The fund also enables municipalities to partner with financial institutions and local businesses to share risk.

The decentralized systems are structured into three modules: drinking water, domestic water, and toilet water. These can be configured based on local needs. In its current commercial phase, the system relies on external sources for drinking water, though the company states it is developing a rainwater purification module that would bring that function fully in-house.

WOTA’s development has been supported by the New Energy and Industrial Technology Development Organization through its Deep Tech Startup Support Fund, and by the Cabinet Office and Ministry of Economy, Trade and Industry through the Small Business Innovation Research program. In 2025, the system passed Technology Readiness Level 6 and is advancing to Level 7, which involves demonstration under actual environmental conditions.

What an Earthquake Does to Central Planning

Japan’s water infrastructure was built primarily during periods of population growth. More than 98 percent of residents have access to safe drinking water through conventional networks. But with population declining and communities shrinking, per capita costs of maintaining extensive pipeline networks have risen sharply.

Natural disasters have added pressure. The 2024 Noto Peninsula earthquake damaged water systems in affected areas. WOTA deployed its systems in Suzu City shortly after the event to help restore emergency access to safe water. Municipal leaders there have since emphasized the importance of local water autonomy in disaster response.

The Ministry of Land, Infrastructure, Transport and Tourism’s Basic Policy Review Committee on Water and Sewerage Systems has been discussing what it calls a “best-mix” approach that combines centralized and decentralized systems depending on population density and geography. This framework is expected to be reflected in the First Mid-term Plan for National Resilience Implementation, scheduled for formulation in 2025.

The Module That Does Not Exist Yet

The WOTA system has cleared regulatory benchmarks for water quality, but long-term performance data under permanent household use does not yet exist. The technology is entering its first extended field trials in 2026, with results expected over the following 12 to 24 months.

The current configuration also does not produce drinking water from greywater alone. Households must obtain drinking water separately, either from external sources or through a rainwater module still under development. The company states that a fully integrated drinking water system is in progress but provides no timeline for completion.

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