Value Village ／ Everyday know-how
This answer is a draft. It stays unpublished until legal review and source verification are complete.
Water is the first supply to run short after a major earthquake, and in Japan the guidance on how much to keep is specific and widely known. The details — how long bottled water keeps, what the bath is for, how to rotate — are where households go wrong.
| Household | 3 days (minimum) | 7 days (recommended) |
|---|---|---|
| 1 person | 9 L | 21 L |
| 2 people | 18 L | 42 L |
| 4 people | 36 L | 84 L (that is 42 × 2 L bottles) |
[Verify] Per-person figures with the Cabinet Office; outage durations with MHLW water-supply damage reports for 2011 and 2024.
The "best before" date on Japanese bottled water reflects slow evaporation through the bottle, which would make the labelled volume inaccurate under the Measurement Act. Sealed water stored away from heat and sunlight is generally considered drinkable after the date, though taste may change. Long-term storage water (5–10-year) is simply thicker-walled bottles.
Filled tap water keeps its chlorine for about 3 days at room temperature (Tokyo Waterworks). After that, use it for hygiene, not drinking, unless boiled.
It is for flushing and washing. A toilet flush uses 6–13 L depending on the model; one bathtub (about 200 L) covers a family for several days of flushing.
Split between the kitchen, a cupboard on another floor, and the car. A collapsed shelf or a room you cannot enter should not take all of it.
Use rolling stock: drink from the stockpile, replace what you use, keep the total. This keeps the water fresh without a separate "emergency" purchase — see the rolling-stock article.
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https://www.bousai.go.jp/kyoiku/keigen/gensai/index.html
https://www.waterworks.metro.tokyo.lg.jp/kurashi/shitsu/
https://www.mhlw.go.jp/stf/seisakunitsuite/bunya/topics/bukyoku/kenkou/suido/
⚠️ 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.
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.
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