Jokaso: Japan's Septic Tanks Explained for Buyers

One Japanese home in ten treats its own wastewater

Japan's wastewater coverage looks excellent on paper: at the end of fiscal 2024, 93.7 % of the population was served by some form of treatment facility, or 116.13 million people (Ministry of the Environment, released 22 August 2025). That headline hides something every rural buyer needs to understand: it is not the same pipe for everyone.

Treatment method	Population served	Share of population
Public sewer (gesuidō, 下水道)	101.40 million	81.8 %
On-site jokaso (jōkasō, 浄化槽)	11.75 million	9.5 %
Rural community sewerage (nōgyō shūraku haisui, 農業集落排水)	2.83 million	2.3 %
Community plants (komyuniti puranto, コミュニティ・プラント)	0.15 million	0.1 %
No treatment at all	about 7.8 million	6.3 %

The countryside is nowhere near 93.7 %

The same survey puts municipalities under 50,000 inhabitants at 84.5 %. Put plainly: the more rural the property, the less likely a public sewer, and the more likely you inherit a private installation to maintain. That is exactly where the cheap stock sits. The akiya listings we track cluster in rural municipalities, where sanitation is the rule rather than the exception. If you are still at the scouting stage, our guide to buying in the Japanese countryside sets the scene; this page covers the one line item almost nobody checks before signing.

A jōkasō (浄化槽, on-site wastewater treatment unit) is not a passive septic tank. It is a small aerated bioreactor: a surface blower called a burowā (ブロワー) pushes air in continuously to feed the bacteria that break down organic matter, and treated water discharges into a ditch or stream. Two consequences follow immediately for the owner: it draws electricity around the clock, and it must be serviced, desludged and inspected, on pain of a fine.

The five sanitation situations, and what each one costs

First, know what you are buying. These are the five cases you will meet on a Japanese listing, from most comfortable to most expensive.

Situation	Term on the listing	What it treats	Cost to the buyer
Public sewer	kōkyō gesuidō (公共下水道)	Everything, off the plot	Usage charge, nothing to maintain
Rural community sewerage	nōgyō shūraku haisui (農業集落排水)	Everything, hamlet plant	Usage charge, sometimes a joining fee
Full-treatment jokaso	gappei shori jōkasō (合併処理浄化槽)	Toilet, kitchen, bath, laundry	¥55,000 to ¥90,000 a year
Toilet-only jokaso	tandoku shori jōkasō (単独処理浄化槽)	Toilet waste only	Maintenance, plus a replacement ahead
Sealed vault, pumped out	kumitori (汲み取り)	Nothing: storage and a tanker truck	Pump-out fees set by the municipality

The word to look for on the listing

On a Japanese fact sheet the line is labelled haisui (排水, drainage) or gesui (下水). A connected property says kōkyō gesuidō; a self-contained one says jōkasō or kumitori. The decisive distinction is rarely spelled out: gappei (合併, full treatment) or tandoku (単独, toilet only). Our article on how to read a Japanese property listing covers the other abbreviations in the same table. When the wording is missing, ask in writing: the gap is worth about a million yen.

Tandoku or gappei: the question worth a million yen

A tandoku shori jōkasō treats toilet water only. All the greywater from the house, kitchen, shower and washing machine, runs straight into the ditch untreated. That is why Japan eventually banned it.

Banned since 2001, yet still everywhere

The amendment to the Septic Tank Act (jōkasō-hō, 浄化槽法) that took effect on 1 April 2001 removed the toilet-only model from the legal definition of a jokaso: not one more can be installed. Existing units were allowed to live out their service life, with a duty on owners to make efforts to convert. Twenty-five years on, the installed base is still enormous.

Jokaso installed in Japan (end of fiscal 2023)	Units	Change over one year
Total	7,455,648	-61,216
Full treatment (gappei)	4,098,165	+74,953
Toilet only (tandoku)	3,357,483	-136,169

Source: Ministry of the Environment, released 7 March 2025. In other words, 45 % of the jokaso still running in Japan are of a type banned from new installation a quarter of a century ago, and the stock is shrinking by roughly 136,000 units a year. Statistically, an older unconnected house you view has close to a one-in-two chance of carrying a unit that will need replacing.

Since 2020, the authorities can force your hand

The reform that took effect on 1 April 2020 created the category of tokutei kizon tandoku shori jōkasō (特定既存単独処理浄化槽): an existing toilet-only unit whose condition, left alone, would seriously threaten public health or the environment. For those, the prefectural governor can advise, then recommend, then order works including removal. In practice a buyer should not think in terms of dealing with it later: a toilet-only tank is a deferred expense, not an option. Treat it as a works line item alongside the roof, in the spirit of our Japan property purchase checklist.

What the law requires of the owner

On completion day you become the jōkasō kanri-sha (浄化槽kanrisha, the person legally responsible for the unit). Those duties are personal and exist independently of any service contract, and the change has to be declared: a change of owner is reported to the municipality or prefecture on a dedicated form, without delay.

Duty	Japanese term	Legal frequency	What it involves
Technical servicing	hoshu tenken (保守点検)	At least 3 times a year	Blower adjustment, disinfectant dosing, sludge checks
Desludging	seisō (清掃)	At least once a year	Accumulated sludge removed by a licensed operator
Commissioning inspection	検査 (Article 7)	Once, between months 3 and 8 of use	Confirms a new unit actually works
Annual inspection	検査 (Article 11)	Every year	Effluent tested by a prefecture-designated body

Servicing and desludging frequencies are set by the Act's enforcement regulation (Articles 6 and 7). The statutory inspection is the duty most often skipped: it is separate from servicing and cannot be carried out by the company that services the unit. Where an owner persistently refuses, the prefecture can order compliance, and breaching that order carries a civil fine of up to ¥300,000 (1,850 €).

The provision that changes everything for an akiya: dormancy

This is the most useful part of the 2020 reform, and almost unknown outside Japan. If the property sits empty, you are not condemned to pay for servicing nobody benefits from: after a full desludging, you file a shiyō kyūshi todoke (使用休止届, notice of suspension of use) with the municipality. While the unit is dormant, the servicing, desludging and annual inspection duties are suspended. On restart, a service visit is carried out immediately beforehand and a restart notice is filed. For a buyer renovating over two years from abroad, the saving runs into hundreds of euros, and the compliance risk drops to zero. This is exactly the kind of paperwork we handle as part of a buying service.

What a jokaso costs: installation, replacement, upkeep

Two separate budgets that should never be blended: the capital cost the day a new unit goes in, and the running cost for as long as the house is lived in.

Installing or replacing

Capacity is measured in ninsō (人槽, population equivalents), and it does not follow the number of actual occupants but the floor area: up to 130 m², a 5-person unit is sufficient; above that, you move to a 7. That is good news for the vast majority of rural Japanese houses, typically between 90 and 130 m².

Item	Cost in yen	In euros
Full-treatment jokaso, 5-person, installed	¥800,000 to ¥1,200,000	4,900 to 7,400 €
Full-treatment jokaso, 7-person, installed	¥1,000,000 to ¥1,400,000	6,200 to 8,600 €
Removing the old tank	¥150,000 to ¥300,000	930 to 1,850 €
Works duration	3 to 7 days	excavation included

These are Japanese renovation market ranges, and access to the plot moves them sharply: a narrow courtyard that keeps the excavator out pushes the bill up. Budget it alongside the rest of the restoration, with the items detailed in our article on the cost of renovating a machiya or kominka.

Running it

Annual item	Cost in yen	In euros
Technical servicing (3 visits)	¥15,000 to ¥24,000	93 to 148 €
Annual desludging	¥32,000 to ¥46,000	198 to 284 €
Statutory annual inspection	about ¥5,000	about 31 €
Blower electricity	¥10,500 to ¥18,900	65 to 117 €
Total	¥55,000 to ¥90,000	340 to 560 €

Neither servicing nor desludging has a nationally regulated tariff: these are market prices, published as guidance by prefectures and municipalities, and many operators offer an all-inclusive annual package that undercuts three separate invoices. Treat the figure as a holding cost, to be added to Japanese property tax and insurance when you compute a yield: our rental yield simulator lets you test it on a specific property.

Municipal subsidies: ¥300,000 to ¥900,000 you can claim back

Replacing an obsolete unit with a full-treatment one serves public policy, so Japan subsidises the work, municipalities first. The scales are municipal, voted each year, and nobody will offer them to you unprompted.

A real scale, as an illustration

The city of Utsunomiya publishes the following grid for fiscal 2026, in areas outside the public sewer network:

Subsidised item	5-person unit (up to 130 m²)	7-person unit (over 130 m²)
Installing the unit	¥425,000 (2,620 €)	¥505,000 (3,120 €)
Removing the old tank	¥150,000 (930 €)	¥150,000 (930 €)
Reworking indoor pipework	¥330,000 (2,040 €)	¥330,000 (2,040 €)

This grid belongs to Utsunomiya and to nobody else: it is quoted here because it is published and verifiable, not because it applies elsewhere. Every municipality votes its own, and a rural town in Wakayama or Chiba will have different figures. The procedure is always the same: call the environment or water department at the town hall, ask for the current year's form, and read the conditions.

The rule that forfeits the subsidy

The application goes in before works begin. A site that has started, even by a day, permanently closes the right to support for that installation. Two further conditions usually apply: the property must be a genuinely occupied dwelling, and the applicant must not be behind on local taxes. This is the single most common reason foreign buyers miss out: they have the work done during the renovation, then discover the scheme six months too late.

Worked example: a ¥3,000,000 akiya in Wakayama

Take a case representative of what our catalogue actually holds: a 110 m² house built in 1994 in a rural Wakayama town, listed at ¥3,000,000 (18,500 €), fitted with its original toilet-only jokaso. The house is otherwise sound. Here is the honest budget.

Item	Yen	Euros
Listed price	¥3,000,000	18,500 €
Acquisition costs (capped at 6 %)	¥180,000	1,110 €
Full-treatment 5-person jokaso, installed	¥950,000	5,860 €
Removing the old tank	¥200,000	1,230 €
Estimated municipal subsidy (typical scale)	-¥575,000	-3,550 €
Total going in	¥3,755,000	23,180 €
Annual upkeep thereafter	¥70,000/yr	430 €/yr

What this table teaches

Sanitation costs ¥575,000 net of subsidy here, or 19 % of the purchase price. On a ¥3,000,000 house that is a major line; on a ¥12,000,000 house it becomes marginal. This is why the cheapest properties are not always the best deals: as the price falls, fixed technical costs weigh proportionally more. The same logic governs one yen akiya, where the purchase price is never the point. If you are comparing several properties in this bracket, our selections of Japanese houses under 50,000 € and kominka for sale let you line those gaps up side by side.

Note what the table does not contain: the subsidy is estimated from a scale published elsewhere. Until the relevant town hall confirms its own in writing, the prudent line is to build the budget without it and treat any grant as upside.

Common mistakes and what to check before signing

The five costliest mistakes

• Reading the word jokaso and stopping there. It does not tell you whether the unit treats the whole house or only the toilet. Without gappei or tandoku, the question is open, and it is worth a million yen.
• Assuming a working unit is a compliant unit. A tank can run for thirty years without ever having seen a statutory inspection. Non-compliance transfers with the house.
• Doing the work before applying for the subsidy. The order of operations cannot be undone.
• Forgetting to register as the new manager. Notify the municipality. Otherwise annual inspection notices keep going out in the seller's name, and nobody answers them.
• Paying to maintain an empty house. The dormancy filing exists precisely for this.

Documents to demand before you offer

Japanese law works in your favour here. Article 35 of the Real Estate Brokerage Act requires the jūyō jikō setsumei (jūyō jikō setsumei, explanation of important matters) to state the condition of the drinking water, electricity, gas and drainage facilities, and, where a facility does not exist, the prospects for connection and any special financial burden that would follow. That is a legal duty of the agency, not a favour: our article on the jūyō jikō setsumei explains how to read it. Ask in addition, in writing, for:

• servicing records for the last three years;
• proof of the most recent desludging;
• the result of the last statutory annual inspection;
• the installation year and exact model of the unit;
• the municipal pump-out tariff, if the property is on a sealed vault.

On a viewing, two simple checks tell you a great deal: listen for the blower running (complete silence is a bad sign) and count the inspection covers in the garden. If you cannot travel, our method for viewing a Japanese property remotely builds these checks into the list handed to the agent.

The special case of a sewer arriving

If the municipality extends its network to your street, connection is not optional. The Sewerage Act requires wastewater to be diverted to the public sewer without delay, and a sealed vault toilet to be converted to a connected flush toilet within three years of the network entering service. A connection contribution voted by the municipality is often added. A well-informed seller knows whether the neighbourhood is on the extension plan: ask, because it changes the next five years of budget.

Conclusion: a technical line item, not a nasty surprise

Sanitation in a Japanese house is neither a detail nor a trap: it is a perfectly quantifiable budget line, provided you look at it before signing rather than after. Three questions close it. Is the property on the public sewer, self-contained, or on a sealed vault? If self-contained, does the unit treat the whole house or only the toilet? And does the municipality subsidise conversion, on what scale, under what conditions?

The answers take two phone calls and a careful reading of the explanation of important matters. They are the difference between a ¥3,000,000 akiya that really costs ¥3,755,000 and a ¥3,000,000 akiya whose bill lands in the first winter. To go further, our Japan property buying guide covers the whole journey from scouting to handover, and the Japanese property listings let you compare real properties with these figures in mind. If you would rather someone inspected the unit and filed the subsidy paperwork with the town hall, that is exactly what our buying service does, and the first conversation is a written exchange with no commitment.

Frequently asked questions

How do I know if a Japanese house is on the public sewer?

The listing carries a drainage line: kōkyō gesuidō means connected to the public sewer, jōkasō means an on-site treatment unit, and kumitori a sealed vault emptied by tanker. If in doubt, the explanation of important matters handed over by the agency must state the condition of the drainage facility.

What is the difference between a gappei and a tandoku jokaso?

A gappei unit treats all the household wastewater, kitchen and bathroom included. A tandoku unit treats toilet waste only, and the greywater leaves untreated. The latter has been banned from new installation since April 2001 and still accounted for 3,357,483 units in service in Japan at the end of fiscal 2023.

How much does annual jokaso maintenance cost?

Between ¥55,000 and ¥90,000 a year (340 to 560 €) for a household unit, adding three servicing visits, one desludging, the statutory inspection and blower electricity. Many operators offer an all-inclusive annual package that comes in below three separately invoiced services.

Can I keep an old toilet-only septic tank?

It may stay in service while it works, but since April 2020 the prefectural governor can recommend and then order its removal where it poses a serious risk to public health or the environment. A careful buyer treats it as a deferred replacement and puts it in the renovation budget.

What should I do with the jokaso of an empty house?

Have it fully desludged, then file a notice of suspension of use with the municipality. The servicing, desludging and annual inspection duties are then suspended until you restart, which avoids paying to maintain a unit nobody is using during a renovation.

Who pays for the replacement, buyer or seller?

In practice the buyer, unless negotiated otherwise. That is precisely why the condition of the unit should be established before you make an offer: a jokaso due for replacement is a quantified negotiating point worth several hundred thousand yen, provided you documented it before committing.

What happens if a public sewer reaches the street?

Connection becomes compulsory: wastewater must be diverted to the public sewer without delay, and a sealed vault toilet must be converted to a connected flush toilet within three years of the network entering service. A connection contribution voted by the municipality is frequently charged on top.