What do people get wrong about reusing bath water (nokoriyu)?
This answer is a draft. It stays unpublished until legal review and source verification are complete.
A Japanese bath holds about 200 litres, and since the family washes before getting in, the water is clean enough to reuse. Most washing machines sold in Japan have a hose to draw from the bath. To visitors this sounds unhygienic; the numbers and the rules explain it.
How it is done
| Item | Detail |
|---|---|
| Bath volume | about 180–220 L for a standard tub |
| Washing machine intake | 50–100 L per load for a top-loader; machines have a bath-water pump hose (furomizu pump) |
| Which cycle | Wash cycle only; rinse with tap water — this is the manufacturers' and government advice |
| When | Same evening or next morning; bacteria increase in warm standing water over 24 hours |
| Not for | Baby clothes, underwear if someone is ill, towels you want odour-free |
| Bath additives | Check the additive's label — some (with sulphur or milky agents) say "not for laundry"; many say "OK for wash cycle, not rinse" |
| Other uses | Toilet flushing (bucket), floor washing, watering plants (if no additives), emergency reserve (see the water-storage article) |
| Savings | 50–100 L per load; about ¥15–30 per load in water and sewer charges at Tokyo rates |
- The Tokyo Waterworks Bureau lists bath-water reuse among household water-saving measures and gives the wash-only rule.
- Bacterial counts in bath water rise roughly tenfold overnight; the wash-only rule and the warm-water benefit make this acceptable for outer clothing, and the tap-water rinse leaves no residue.
- Warm water (about 30–35°C the next morning) dissolves detergent and lifts grease better than cold; Japanese washing machines otherwise use cold water by default.
- Households keep the bath covered overnight to retain warmth and keep dust out; the tub is the household's emergency water in a quake (200 L for flushing).
[Verify] Water-saving figures with the Tokyo Waterworks Bureau; bacterial data with consumer-testing reports (e.g. Kokusen); additive guidance on product labels.
Misunderstanding 1｜It is dirty water
The family washes before entering; the water is warm, soap-free and lightly used. It is used for the wash, not the rinse, and the rinse is tap water.
Misunderstanding 2｜Use it for everything, including the rinse
The rinse is tap water so no residue or odour remains. Wash-only is the rule from manufacturers, waterworks and consumer bodies.
Misunderstanding 3｜Leave the water for a couple of days
Bacteria multiply in warm standing water; use it the same evening or the next morning, then drain and clean the tub.
Misunderstanding 4｜Bath additives make no difference
Some additives stain fabric or damage the pump. Read the additive's label for a laundry statement; many list it explicitly.
Misunderstanding 5｜The saving is trivial
50–100 L per load, every day, for a family is 20–35 m³ a year — a meaningful share of household water. And the warm wash cleans better.
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Sources
- Tokyo Waterworks Bureau — Water-saving at home (bath-water reuse)
https://www.waterworks.metro.tokyo.lg.jp/kurashi/setsusui/
- Japan Electrical Manufacturers' Association — Washing machines with bath-water pumps
https://www.jema-net.or.jp/
- Tokyo Metropolitan Government Bureau of Public Health — Household hygiene and standing water
https://www.hokeniryo.metro.tokyo.lg.jp/kankyo/
⚠️ Editorial note: the source URLs above were identified by search. Our working environment cannot reach go.jp domains, so the contents have not been checked against the text. Verify every source before publication and record who checked it and when.
About this article
What we share here are ideas and everyday practices passed down among people living in Japan, together with general information drawn from public sources. They are not official recommendations, and they are not professional instruction. Practices vary between households and regions.
This is general information. Results vary from person to person and depend on your own conditions and surroundings.
Please decide for yourself, using your own judgement, whether any of this suits your situation. We cannot accept responsibility for any damage, loss or injury arising from following this article.
Always follow the instructions on any product you use, and never mix cleaning products. If you rent your home, check with your landlord before making any changes.
Sources
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