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B1 noun #6,000 most common 9 min read

汚水

Top 6,000

Practice it Examples Notes & Tips 汚水 in 30 Seconds

Explanation 汚水 in your Level:

At the A1 level, you don't need to use the word '汚水' (osui) very often. It is a bit too technical for basic greetings and simple shopping. However, it is good to recognize the first kanji '水' (mizu), which means water. At this stage, you would usually just say 'kitanai mizu' (dirty water) if you saw a puddle. '汚水' is a word you might see on a sign near a drain or a manhole cover in Japan. Think of it as a 'danger' or 'keep away' sign. You don't need to produce this word in your own speaking yet, but knowing that 'sui' at the end of a word often relates to water will help you build your vocabulary later on. Just remember: 'osui' is water that is not clean and usually comes from a pipe.

At the A2 level, you are starting to talk more about your daily life and your surroundings. You might encounter '汚水' (osui) when talking about housework or the city you live in. For example, if you are explaining that you are washing dishes, you might think about where the water goes. In Japan, the water that goes down the drain is called '汚水.' You might see this word on your monthly water bill (suido-dai), which is divided into 'clean water' (jousui) and 'wastewater' (osui). Learning this word helps you understand how Japanese cities work. You can start to use it in simple sentences like 'Osui o nagashimasu' (I drain the wastewater), although 'mizu o nagashimasu' is still more common in daily speech.

At the B1 level, you are expected to handle more complex topics like the environment and social issues. This is where '汚水' (osui) becomes a very important word. You will use it to discuss pollution, factory waste, and environmental protection. For example, if you are writing an essay about saving the earth, you would use '汚水' to describe the sewage that pollutes rivers. You should also know common verb pairings like 'osui o shori suru' (to treat sewage). At this level, you can distinguish between 'osui' (the polluted liquid) and 'gesui' (the sewage system). Being able to use this word correctly shows that you have moved beyond basic survival Japanese and can now participate in discussions about more serious, adult topics.

At the B2 level, you should be comfortable using '汚水' (osui) in professional or academic contexts. You might read news articles about 'osui shori' (wastewater treatment) technologies or government policies regarding 'osui no haishutsu' (discharge of polluted water). You should understand the nuances between 汚水 and similar words like 排水 (haisui - drainage) and 廃液 (haieki - waste liquid). In a debate about industrialization, you could argue about the cost of managing 汚水. You should also be familiar with compound words like '汚水処理施設' (wastewater treatment facility). Your usage should be precise, using 'osui' when referring to the quality of the water as being contaminated by human or industrial waste.

At the C1 level, you are expected to understand the legal and scientific nuances of '汚水' (osui). This includes knowing how the term is defined in the 'Sewerage Act' (下水道法) and the 'Water Pollution Control Act' (水質汚濁防止法). You might encounter this word in high-level business negotiations involving manufacturing or urban development. You should be able to discuss the chemical composition of 汚水 or the biological oxygen demand (BOD) associated with it in a technical report. At this level, you might also encounter the word in literary contexts, where it could be used metaphorically to describe societal decay or moral corruption, though its primary use remains technical. Your ability to use 'osui' correctly in a variety of formal registers is a mark of high proficiency.

At the C2 level, your mastery of '汚水' (osui) is near-native. You understand its historical development as a term in Japanese urban planning from the Meiji era to the present. You can navigate complex legal documents that use 'osui' to define liability in environmental law cases. You are also aware of the subtle cultural connotations of 'impurity' that the word carries, linking back to traditional Japanese views on water and cleanliness. You can effortlessly switch between technical jargon and more common phrasing, depending on your audience. Whether you are presenting at an international conference on water management or reading a dense sociological critique of urban infrastructure, you understand every nuance and implication of the word '汚水'.

Practice it Examples Notes & Tips

汚水 in 30 Seconds

汚水 (osui) is the formal Japanese term for polluted water, wastewater, or sewage resulting from human, domestic, or industrial activities.
It is primarily used in technical, environmental, and administrative contexts rather than casual conversation about everyday spills or muddy water.
Key associations include wastewater treatment plants (汚水処理場), environmental pollution, and urban infrastructure like sewage pipes and manholes.
Grammatically, it is a noun that often pairs with verbs like 'treat' (処理する), 'discharge' (排出する), and 'purify' (浄化する).

The Japanese word 汚水 (おすい - osui) is a compound noun that literally translates to 'dirty water' or 'polluted water.' In a technical and everyday context, it refers specifically to water that has been contaminated by human activity, industrial processes, or household use. This is not just water with a bit of mud in it; it is the formal term for sewage, wastewater, and effluent that requires treatment before it can be safely returned to the environment. When you see this word, think of the infrastructure of a city—the pipes beneath the streets, the treatment plants on the outskirts, and the environmental regulations that keep rivers clean. It is a word that sits at the intersection of environmental science, urban planning, and daily hygiene.

Technical Definition: In the context of Japanese sewage law, 汚水 refers to liquid waste discharged from toilets, kitchens, baths, and industrial facilities. It is distinguished from 'rainwater' (雨水 - usui) in modern 'separate' sewage systems.

この工場は適切に汚水を処理していない疑いがある。 (There is a suspicion that this factory is not properly treating its polluted water.)

The nuance of 汚水 is quite clinical and formal. While a child might say 'kitanai mizu' (dirty water) to describe a puddle, an engineer, a government official, or a concerned citizen at a town hall meeting would use 'osui.' It carries a weight of responsibility and hazard. In Japan, a country with high rainfall and dense urban populations, the management of 汚水 is a massive public works priority. The word appears frequently in bills for utility services, on manhole covers (though often abbreviated or implied), and in news reports concerning environmental protection. Understanding this word helps you navigate the more serious side of Japanese society—its commitment to public health and ecological preservation.

Etymology Breakdown: The first kanji 汚 (o/kegare) represents 'dirty,' 'polluted,' or 'disgrace.' The second kanji 水 (sui/mizu) is the universal symbol for 'water.' Together, they form a clear, logical concept of water that has lost its purity.

地震の影響で、汚水が道路に溢れ出した。 (Due to the earthquake, sewage began to overflow onto the roads.)

Culturally, Japan has a deep-seated respect for clean water, rooted in Shinto purification rituals. Therefore, 汚水 is not just a physical nuisance but a conceptual opposite to the 'pure' state that society strives to maintain. This is why the Japanese government enforces strict 'Water Pollution Control Laws' (水質汚濁防止法). When discussing environmental issues, 汚水 is the primary term used to describe the source of river and ocean degradation. Whether it is 'domestic wastewater' (生活汚水) or 'industrial wastewater' (工場汚水), the term remains the standard for any water that has been tainted by use and requires remediation.

Using 汚水 correctly requires understanding its role as a formal noun. It is rarely used in casual conversation to describe a spilled drink or a muddy pond. Instead, it functions as a technical descriptor in contexts of infrastructure, environmentalism, and public health. It often pairs with verbs like 処理する (shori suru - to treat/process), 流す (nagasu - to pour/drain), or 漏れる (moreru - to leak). Because it is a Sino-Japanese (Kango) word, it carries a professional and objective tone.

Common Verb Pairings: 汚水を処理する (Treat sewage), 汚水を排出する (Discharge wastewater), 汚水を浄化する (Purify polluted water).

家庭から出る汚水は、下水道を通って処理場へ運ばれます。 (The wastewater coming from homes is carried through the sewage system to the treatment plant.)

When talking about environmental damage, 汚水 is often the subject of the sentence. For example, 'The river was contaminated by 汚水.' In this case, it emphasizes the substance itself as the pollutant. In administrative contexts, you will see it used in compounds like 汚水処理施設 (osui shori shisetsu - wastewater treatment facility). If you are living in Japan and have a problem with your plumbing that involves 'foul water' backing up, you would use this term when calling a professional or explaining the situation to a landlord to sound precise and clear about the severity of the issue.

未処理の汚水を海に流すことは法律で禁じられている。 (Discharging untreated sewage into the ocean is prohibited by law.)

In more advanced usage, 汚水 can be used metaphorically, though this is less common than its literal meaning. It might appear in literature to describe a 'polluted' or 'corrupt' stream of thought or a 'filthy' social situation, but 'osui' remains predominantly a term of physical science and urban management. If you want to describe a person's character as 'dirty,' you would use 'fuketsu' or 'kitanai,' not 'osui.' Always stick to the literal meaning of water that has been used and contaminated to ensure your Japanese sounds natural and professional.

In daily Japanese life, 汚水 is a word you are more likely to read or hear in formal announcements than in a casual chat over coffee. However, its presence is constant in the background of a functioning society. You will hear it on the NHK evening news during reports on environmental regulations or natural disasters. For instance, after a heavy typhoon, news anchors might report on 汚水 overflows in certain wards. You will also encounter it in documentaries about 'SDGs' (Sustainable Development Goals), specifically regarding clean water and sanitation (Goal 6).

In the Media: News reports on 'Blue-Green Algae' or 'Red Tide' often cite the discharge of 汚水 as a primary cause of nutrient loading in lakes and bays.

ニュース：『大雨により、一部の地域で汚水が溢れる被害が出ています。』 (News: "Due to heavy rain, there is damage from sewage overflowing in some areas.")

Another common place is in 'City Newsletters' (広報 - kouhou) or on your water bill. Japanese municipalities are very transparent about where your tax money goes, and '汚水処理費' (wastewater treatment fees) is a standard line item. If you visit a science museum or an environmental center in Japan, the exhibits explaining the 'Water Cycle' (水の循環) will invariably use the term 汚水 to describe the stage between human consumption and the purification process. It's a word that signifies the unseen work that keeps a modern city livable.

科学館の展示：『私たちは毎日、大量の汚水を出しています。』 (Science Museum Display: "We produce a large amount of wastewater every day.")

Finally, in the business world, especially in manufacturing or real estate, 汚水 is a critical term. Real estate listings might mention if a property is connected to the 'public sewage system' (公共下水道) or if it uses a 'private septic tank' (浄化槽) to treat 汚水. For factory managers, monitoring the quality of 汚水 is a daily legal requirement. Therefore, if you work in any technical or administrative field in Japan, this word is indispensable. It represents the 'output' of civilization that must be managed with care and precision.

The most common mistake learners make with 汚水 is using it in contexts where 'dirty' is simply an adjective rather than a technical classification. For example, if you see a glass of water with some dust in it, calling it 汚水 sounds incredibly dramatic and technically incorrect—it’s just 'kitanai mizu.' 汚水 implies a level of contamination that usually involves chemical or biological waste. Another mistake is confusing 汚水 (the water itself) with 下水 (gesui - the sewage system or the general concept of sewage).

Osui vs. Gesui: 汚水 is the substance (the liquid). 下水 is the infrastructure (the pipes and system). While people often use 'gesui' to mean the water too, 'osui' is more specific to the liquid's state of pollution.

❌ このコップの水は汚水です。 (Wrong: This cup of water is industrial sewage.)
✅ このコップの水は汚れています。 (Right: This cup of water is dirty.)

Another nuance error is confusing 汚水 with 泥水 (doromizu - muddy water). If a river is brown because of a storm, it is 泥水. If it is brown because a chemical plant dumped waste into it, it is 汚水. Use 汚水 when the 'dirtiness' is a result of human-induced pollution or waste. Furthermore, learners sometimes mispronounce it as 'okusui' or 'osui' with the wrong pitch. The pitch accent is generally 'Heiban' (flat), meaning the syllables stay relatively level, though regional variations exist.

❌ 彼は汚水のような男だ。 (Wrong/Strange: He is a man like sewage.)
✅ 彼は卑劣な男だ。 (Right: He is a despicable man.)

Lastly, be careful with the kanji. The first kanji 汚 is also used in 汚れる (yogoreru - to get dirty) and 汚す (yogosu - to make dirty). However, in the compound 汚水, it uses the 'on-yomi' reading 'O.' Don't say 'yogoremizu.' Using the wrong reading is a common beginner mistake that immediately marks you as a non-native speaker. Stick to the 'O-SUI' reading for all formal and technical contexts.

In Japanese, there are several words for 'dirty water,' each with a specific domain. Choosing the right one depends on whether you are talking about a kitchen sink, a factory pipe, or a muddy puddle. 汚水 is the broadest technical term, but let's look at its neighbors to understand where it fits in the linguistic landscape. The most common alternative is 排水 (haisui), which means 'drainage.' While 排水 is often dirty, the word itself just refers to water being moved out of a system.

汚水 vs. 排水 (Haisui): 汚水 emphasizes the quality (it is polluted). 排水 emphasizes the action (it is being drained). All sewage is 汚水, but not all 排水 is necessarily 汚水 (e.g., clean cooling water).

工場の排水口から、汚水が流れ出している。 (Polluted water is flowing out of the factory's drainage outlet.)

Another related term is 下水 (gesui). As mentioned before, this refers to the sewage system. In many cases, people use 下水 to refer to the water itself, but in a technical report, 汚水 is preferred for the liquid. Then there is 濁水 (dakusui), which means 'turbid water' or 'cloudy water.' This is used for water that is physically cloudy with silt or sand, often after a storm or near a construction site. It doesn't necessarily imply the presence of harmful chemicals like 汚水 does.

Other Alternatives: 廃液 (Haieki): Specifically 'waste liquid,' often used for chemical or medical waste.
汚濁水 (Odakusui): A very formal term for highly contaminated water, often used in environmental reports.

川の濁水を調査した結果、有害な汚水が含まれていることがわかった。 (As a result of investigating the turbid river water, it was found to contain harmful sewage.)

Finally, for everyday 'dirty water' (like water after washing a car), simply saying 'kitanai mizu' or 'yogoreta mizu' is most natural. Using 汚水 in your backyard feels like you're writing a government report. By understanding these distinctions, you can navigate Japanese conversations about nature, urban life, and technology with the precision of a native speaker. Remember: 汚水 is for the system, the environment, and the law; 'kitanai mizu' is for your daily life.

How Formal Is It?

Fun Fact

The kanji 汚 originally depicted a person bending over (to wash or deal with dirt) next to water. It highlights the human element in making things dirty.

Pronunciation Guide

UK /ɒˈsuːi/

US /oʊˈsuːi/

The pitch accent is 'Heiban' (Type 0). This means the pitch starts low and rises, then stays high for the rest of the word.

Rhymes With

Kosui (Lake water) Yosui (Irrigation water) Josui (Clean water) Gensui (Water level reduction) Kansui (Completion/Flooding) Shinsui (Soaking) Tensui (Rainwater) Bunsui (Water shed)

Common Errors

Pronouncing it as 'oshoo-ee' (mixing up 'su' and 'shu').
Using a falling pitch on the 'sui'.
Reading the first kanji as 'yogore' instead of 'o'.
Elongating the 'o' sound too much.
Stressing the 'su' like the English word 'sue'.

Difficulty Rating

Reading 3/5

The kanji are standard (Grade 6 and Grade 1), but the 'O' reading for 汚 must be learned specifically for compounds.

Writing 3/5

Writing 汚 requires attention to the stroke order and the right-hand side components.

Speaking 2/5

The pronunciation 'osui' is simple, but the pitch must be kept flat.

Listening 2/5

Easily recognized in news and formal contexts due to its distinct sound.

What to Learn Next

Prerequisites

水 (Water) 汚い (Dirty) 流す (To flow/pour) 処理 (Processing) 川 (River)

Learn Next

排水 (Drainage) 浄化 (Purification) 下水道 (Sewage system) 環境保護 (Environmental protection) 汚染 (Pollution)

Advanced

水質汚濁防止法 (Water Pollution Control Act) 生物化学的酸素要求量 (BOD) 活性汚泥法 (Activated sludge process)

Grammar to Know

Kango Compounds

汚 (O) + 水 (Sui) = 汚水 (Osui). Many technical terms follow this pattern.

Causative Passive

汚水が流される (Wastewater is made to flow).

Compound Nouns

汚水処理場 (Osui + Shori + Jou = Wastewater treatment place).

Formal Nominalization

汚水の排出 (The discharge of wastewater).

Transitive vs. Intransitive

汚水が流れる (intransitive) vs. 汚水を流す (transitive).

Examples by Level

これは汚水です。

This is polluted water.

Simple A is B structure.

汚水にさわらないでください。

Please do not touch the polluted water.

Using -naide kudasai for prohibition.

汚水はどこへ行きますか？

Where does the wastewater go?

Basic question with 'doko'.

汚水はきれいにします。

We make the polluted water clean.

Verb 'kirei ni suru' meaning 'to make clean'.

ここは汚水の出口です。

This is the outlet for polluted water.

Possessive 'no' connecting two nouns.

汚水はくさいです。

The wastewater is smelly.

I-adjective 'kusai' used as a predicate.

汚水がたくさんあります。

There is a lot of polluted water.

Using 'takusan' to indicate quantity.

汚水を見ました。

I saw polluted water.

Past tense of 'miru'.

台所から汚水が流れます。

Wastewater flows from the kitchen.

Source particle 'kara' and intransitive verb 'nagareru'.

汚水をきれいにしましょう。

Let's clean the polluted water.

Volitional form '-mashou'.

汚水が道に溢れています。

Sewage is overflowing onto the road.

Continuous state '-te iru'.

この町は汚水を処理しています。

This town treats its sewage.

Object marker 'o' with 'shori suru'.

汚水の臭いが気になります。

I am bothered by the smell of sewage.

Phrase 'ki ni naru' (to be bothered/mind).

汚水は川に流してはいけません。

You must not pour wastewater into the river.

Prohibition '-te wa ikemasen'.

地震で汚水管が壊れました。

The sewage pipe broke due to the earthquake.

Cause particle 'de' and past tense of 'kowareru'.

汚水の処理にはお金がかかります。

It costs money to treat wastewater.

Verb 'kakaru' used for cost.

工場が汚水を海に直接流している。

The factory is pouring polluted water directly into the sea.

Adverb 'chokusetsu' (directly).

汚水処理の技術が向上しました。

Wastewater treatment technology has improved.

Noun 'koujou' (improvement) used as a verb.

生活汚水が川を汚す原因の一つです。

Domestic wastewater is one of the causes of river pollution.

Compound 'seikatsu osui' (domestic wastewater).

キャンプ場では汚水の処理に注意してください。

Please be careful with wastewater disposal at the campsite.

Particle 'ni' indicating the object of attention.

汚水が地下水に混ざる恐れがあります。

There is a fear that sewage will mix with groundwater.

Phrase 'osore ga aru' (there is a fear/risk).

この地域は汚水と雨水を分けています。

This area separates sewage and rainwater.

Verb 'wakeru' (to separate).

汚水に含まれる有害物質を調査する。

We will investigate the harmful substances contained in the wastewater.

Passive-like structure 'ni fukumareru' (contained in).

汚水処理場を見学に行きました。

I went to visit a wastewater treatment plant.

Noun 'kengaku' (study visit).

環境基準を超える汚水が検出された。

Polluted water exceeding environmental standards was detected.

Verb 'koeru' (to exceed) and 'kenshutsu sareru' (to be detected).

汚水の排出規制が厳しくなっています。

Regulations on wastewater discharge are becoming stricter.

Noun 'kisei' (regulation) and 'kibishiku naru' (become strict).

新しい住宅地には汚水処理施設が必要です。

A wastewater treatment facility is necessary for the new residential area.

Adjective 'hitsuyou' (necessary).

汚水を再利用するシステムを導入した。

We introduced a system to reuse wastewater.

Noun 'dounyuu' (introduction/implementation).

洪水で汚水処理機能が停止してしまった。

The wastewater treatment function stopped due to the flood.

Auxiliary verb '-te shimau' showing regret/completion.

住民は汚水の臭いに対して苦情を申し立てた。

Residents filed a complaint regarding the smell of the sewage.

Structure 'ni taishite' (towards/regarding).

汚水の中に大量のプラスチックゴミが混じっていた。

A large amount of plastic waste was mixed in the sewage.

Verb 'majiru' (to be mixed).

この会社は汚水の浄化技術で特許を取った。

This company obtained a patent for wastewater purification technology.

Noun 'tokkyo' (patent).

高度汚水処理プロセスにより、水質が大幅に改善された。

The water quality has significantly improved due to the advanced wastewater treatment process.

Compound 'koudo osui shori' (advanced wastewater treatment).

汚水の不法投棄は、生態系に深刻なダメージを与える。

Illegal dumping of sewage causes serious damage to the ecosystem.

Noun 'fuhou touki' (illegal dumping).

都市計画において、汚水管理は極めて重要な課題である。

In urban planning, wastewater management is an extremely important issue.

Adverb 'kiwamete' (extremely).

汚水処理に伴うエネルギー消費の削減が求められている。

Reduction of energy consumption associated with wastewater treatment is being demanded.

Structure 'ni tomonau' (accompanying/associated with).

放射性物質を含む汚水の処理方法が議論されている。

Methods for treating wastewater containing radioactive substances are being discussed.

Verb 'fukumu' (containing).

汚水からのリン回収技術は、資源循環の観点から注目されている。

Technology for recovering phosphorus from wastewater is attracting attention from a resource circulation perspective.

Structure 'no kanten kara' (from the perspective of).

下水道法に基づき、汚水の水質検査が定期的に実施される。

Based on the Sewerage Act, water quality inspections of sewage are periodically conducted.

Structure 'ni motozuki' (based on).

汚水処理施設の老朽化が、多くの地方自治体で問題となっている。

The aging of wastewater treatment facilities has become a problem in many local municipalities.

Noun 'roukyuuka' (aging/deterioration).

汚水処理の未整備が、公衆衛生上の大きな懸念材料となっている。

The lack of wastewater treatment infrastructure is a major public health concern.

Noun 'miseybi' (lack of infrastructure).

産業汚水の排出基準を厳格化する法案が可決された。

A bill to tighten discharge standards for industrial wastewater was passed.

Verb 'genkakuka' (tightening/making strict).

汚水処理における微生物の役割は、極めて多岐にわたる。

The role of microorganisms in wastewater treatment is extremely diverse.

Adjective 'takini wataru' (diverse/wide-ranging).

越境汚染の問題を解決するため、汚水管理の国際協力が不可欠だ。

International cooperation in wastewater management is essential to solve the problem of transboundary pollution.

Noun 'ekkyou osen' (transboundary pollution).

汚水スラリーの有効活用は、持続可能な社会の実現に寄与する。

The effective utilization of sewage slurry contributes to the realization of a sustainable society.

Verb 'kiyo suru' (to contribute).

都市のレジリエンスを高めるには、強靭な汚水処理インフラが欠かせない。

To increase urban resilience, robust wastewater treatment infrastructure is indispensable.

Noun 'rejiriensu' (resilience).

汚水処理の過程で発生するメタンガスを燃料として回収する。

Methane gas generated during the wastewater treatment process is recovered as fuel.

Structure 'no katei de' (in the process of).

汚水管理の歴史を紐解くと、近代都市の発展の軌跡が見えてくる。

Unraveling the history of wastewater management reveals the trajectory of modern urban development.

Verb 'himotoku' (to unravel/read a book).

Common Collocations

汚水処理

汚水処理場

汚水管

汚水槽

汚水排出

汚水浄化

汚水漏れ

生活汚水

工業汚水

未処理汚水

Common Phrases

汚水を流す

— To drain or discharge wastewater.

汚水を川に流してはいけない。

汚水が溢れる

— Sewage overflows.

大雨で汚水が溢れた。

汚水を処理する

— To treat wastewater or sewage.

適切に汚水を処理する。

汚水の臭い

— The smell of sewage.

汚水の臭いが漂っている。

汚水を浄化する

— To purify polluted water.

汚水を浄化して再利用する。

汚水の影響

— The impact of polluted water.

汚水の影響で魚が死んだ。

汚水の検査

— Inspection/testing of wastewater.

汚水の水質検査を行う。

汚水の管理

— Management of wastewater.

汚水の管理を徹底する。

汚水の放出

— Release of wastewater.

汚水の放出を止める。

汚水対策

— Countermeasures against wastewater pollution.

汚水対策を講じる。

Often Confused With

汚水 vs 下水 (Gesui)

Gesui is the whole system/infrastructure; Osui is specifically the dirty water.

汚水 vs 排水 (Haisui)

Haisui is any water being drained; Osui is water that is definitely polluted.

汚水 vs 濁水 (Dakusui)

Dakusui is cloudy water (often natural); Osui is polluted water (often man-made).

Idioms & Expressions

"汚水にまみれる"

— To be covered in sewage; used literally or to describe a very messy situation.

作業員は汚水にまみれて修理した。

Literary/Descriptive

"汚水の溜まり場"

— A place where sewage collects; sometimes used to describe a corrupt place.

そこは社会の汚水の溜まり場だ。

Metaphorical

"汚水を注ぐ"

— To pour sewage; can imply adding insult to injury or ruining something pure.

清流に汚水を注ぐような行為だ。

Metaphorical

"汚水のごとく"

— Like sewage; used to describe something flowing or spreading in a disgusting way.

汚水のごとく悪評が広まった。

Literary

"汚水を飲み干す"

— To drink sewage; used to describe enduring extreme hardship or humiliation.

汚水を飲み干すような思いで耐えた。

Metaphorical

"汚水の中の蓮"

— A lotus in sewage; similar to 'lotus in the mud,' meaning something pure in a corrupt world.

彼女は汚水の中の蓮のような存在だ。

Poetic

"汚水を分ける"

— To separate sewage; implies making a clear distinction between right and wrong.

善悪を汚水を分けるように明確にする。

Rare/Metaphorical

"汚水に足を突っ込む"

— To step into sewage; to get involved in a dirty or corrupt business.

汚水に足を突っ込む覚悟はあるか？

Idiomatic

"汚水が澄むことはない"

— Sewage never clears; used to say that something inherently bad will never become good.

汚水が澄むことはないように、彼の本性は変わらない。

Proverbial

"汚水を清める"

— To cleanse sewage; to attempt to fix a deeply corrupt or broken system.

政治の汚水を清めるのは容易ではない。

Metaphorical

Easily Confused

汚水 vs 泥水 (Doromizu)

Both are 'dirty' water.

Doromizu is water with mud/dirt (natural). Osui is water with waste/pollution (man-made).

雨で道が泥水だらけだ。

汚水 vs 雨水 (Usui/Amamizu)

They sound similar (Osui vs. Usui).

Usui is rainwater. Osui is sewage. Modern cities separate them.

雨水を貯めて庭にまく。

汚水 vs 廃液 (Haieki)

Both are waste liquids.

Haieki is usually chemical or medical waste in small/concentrated amounts. Osui is general wastewater in large volumes.

実験の廃液を回収する。

汚水 vs 汚濁 (Odaku)

Related to pollution.

Odaku is the noun for 'contamination/pollution' (the state). Osui is the actual water.

河川の汚濁が進んでいる。

汚水 vs 汚物 (Obutsu)

Both mean 'filth'.

Obutsu refers to solid waste, trash, or excrement. Osui is liquid waste.

汚物を適切に処理する。

Sentence Patterns

これは[Noun]です。

これは汚水です。

[Noun]を[Verb]ます。

汚水を流します。

[Noun]は[Noun]の原因です。

汚水は汚染の原因です。

[Noun]が[Verb-Passive]されています。

汚水が処理されています。

[Noun]に基づき、[Noun]が行われる。

法律に基づき、汚水の検査が行われる。

[Noun]の[Noun]は、[Noun]に寄与する。

汚水の再利用は、持続可能な社会に寄与する。

[Noun]の恐れがある。

汚水が漏れる恐れがある。

[Noun]を[Verb-Causative]必要がある。

汚水を浄化させる必要がある。

Word Family

Nouns

汚染 (Osen - Pollution)

汚物 (Obutsu - Filth/Excrement)

汚名 (Omei - Stigma/Dishonor)

汚職 (Oshoku - Corruption)

Verbs

汚す (Yogosu - To make dirty)

汚れる (Yogoreru - To get dirty)

汚染する (Osen suru - To pollute)

Adjectives

汚い (Kitnai - Dirty)

汚らわしい (Kegarawashii - Filthy/Abominable)

下水 (Gesui)

排水 (Haisui)

浄化 (Jouka)

環境 (Kankyou)

水質 (Suishitsu)

How to Use It

frequency

Common in news, utility bills, and environmental discussions. Rare in casual social chats.

Common Mistakes

Using 'osui' for a muddy puddle. → Doromizu (泥水).
Osui implies pollution/waste, while doromizu is just natural mud.
Pronouncing it as 'yogoremizu'. → Osui (汚水).
In compounds, the 'on-yomi' reading 'O' is used, not the 'kun-yomi' 'yogore'.
Calling a dirty person 'osui'. → Kitanai hito / Fuketsu na hito.
Osui is only for literal water, not a metaphorical description of people.
Confusing 'osui' with 'usui'. → Osui (sewage) vs Usui (rainwater).
They sound similar but are opposites in urban planning.
Using 'osui' for chemical waste in a lab. → Haieki (廃液).
Haieki is more specific for concentrated chemical waste liquids.

Tips

The 'O' No! Water

Think of 'O' as an exclamation of disgust when you see dirty water (Sui). 'O-Sui!'

Verb Pairing

Always remember 'osui o shori suru' (treat sewage). It's the most common phrase you'll hear in professional contexts.

Manhole Spotting

Look for the kanji 汚 on manhole covers in Japan. It's a great way to see the word in the real world.

Technical vs. Casual

Avoid using 'osui' for small messes. If you spill juice, it's not 'osui,' it's just 'yogore.'

News Keywords

In news about typhoons, listen for 'osui' to know if the sewers are overflowing.

Kanji Parts

The left side of 汚 is the water radical. The right side is 'ku' (square/bent). Think of water being 'bent' or 'distorted' from its pure state.

Flat Pitch

Don't emphasize any syllable. 'o-su-i' should sound like a single, level unit of sound.

SDGs

If you talk about Sustainable Development Goals in Japanese, 'osui' is a key vocabulary word for Goal 6.

Antonym Recall

Remember 'jousui' (clean tap water) as the opposite of 'osui' (wastewater).

Compound Power

Learn 'osui shori' as a single block. It's much more useful than just 'osui' alone.

Memorize It

Mnemonic

Think of 'O' as 'Oh no!' and 'SUI' as 'Suicide' (for the environment). 'Oh no, the water is killing the environment!' = 汚水 (Osui).

Visual Association

Imagine a dark, murky pipe (汚) pouring into a clear blue stream (水). The contrast represents 汚水.

Word Web

Pipe Smell Factory Toilet Clean Filter River Law

Challenge

Try to find the word 汚水 on five different manhole covers or utility boxes next time you walk through a Japanese city.

Word Origin

The word '汚水' is a Kango (Sino-Japanese word) composed of two characters. '汚' (O) traces back to the concept of stagnant or muddy water that stains. '水' (Sui) is the pictograph for flowing water.

Original meaning: Water that is stagnant and has become foul or stained.

Sino-Japanese (Kango).

Cultural Context

While 汚水 is a technical term, be mindful that discussing sewage can be considered impolite at the dinner table. Use 'mizu' or 'suido' instead if the topic is not technical.

In English-speaking countries, we often just say 'sewage' or 'wastewater.' 'Polluted water' sounds more like an environmental disaster. In Japanese, 汚水 covers all these bases neutrally.

The film 'Spirited Away' features a 'Stink Spirit' who is actually a polluted river spirit filled with 汚水 and trash. Minamata Disease documentaries frequently use the term 汚水 to describe the industrial mercury discharge. NHK's 'Project X' has an episode about the development of Japan's sewage systems.

Practice in Real Life

Real-World Contexts

Domestic Life

汚水が詰まる
汚水処理費
生活汚水を減らす
汚水の臭い

Environmentalism

汚水による汚染
汚水の浄化
汚水排出基準
川に汚水を流す

Urban Infrastructure

汚水管の工事
汚水処理施設
公共下水道
汚水ポンプ

Industry

工場汚水の処理
汚水の再利用
不法投棄
排出規制

Natural Disasters

汚水が溢れる
汚水管の破裂
避難所の汚水対策
洪水と汚水

Conversation Starters

"最近、近所の川の汚水問題がニュースになっていますね。"

"日本の汚水処理技術は世界でもトップクラスだそうですよ。"

"環境のために、生活汚水を減らすにはどうすればいいと思いますか？"

"あなたの国では、汚水の処理はどのように行われていますか？"

"このマンションの汚水処理費用、少し高い気がしませんか？"

Journal Prompts

今日、街を歩いていて汚水の臭いや看板に気づいたことはありますか？

もし汚水処理が止まってしまったら、私たちの生活はどう変わるでしょうか？

環境を守るために、自分が今日からできる汚水対策について書いてください。

工場の汚水問題について、経済発展と環境保護のどちらを優先すべきだと思いますか？

水の大切さと、汚水をきれいにする技術の進化について感じたことを書いてください。

Frequently Asked Questions

10 questions

Usually, no. You would just say 'yogoreta mizu.' 'Osui' sounds too industrial or like sewage for a pet context.

No. Rainwater is 'usui' (雨水). In Japan, 'osui' (sewage) and 'usui' (rainwater) are often handled by separate pipe systems.

'Osui' is the water itself (polluted water). 'Gesui' refers to the sewage system or the general concept of wastewater management.

No, it's a technical, medical, and environmental term. It's not a swear word, though it describes something unpleasant.

It is written as 汚 (dirty) and 水 (water). 汚水.

No. That would sound very strange and wouldn't be understood as an insult. Use 'kitanai' or 'fuketsu'.

Yes, in Japan, water bills often show 'osui shori-dai' (wastewater treatment fee) alongside 'suido-dai' (water usage fee).

It is a wastewater treatment plant. It's the facility where sewage is cleaned before being released.

Yes, it's the standard term in environmental science for effluent or contaminated water.

It's pronounced 'oh-sue-ee' with the pitch remaining flat across all syllables.