What do people get wrong about drinking water (hydration)?

This answer is a draft. It stays unpublished until legal review and source verification are complete.

"Two litres a day" is a number that travels the world on its own. Material from Japan's Ministry of Health, Labour and Welfare (MHLW) gives a more detailed breakdown, and it changes what the number means. In Japan's hot, humid summers the question is far from academic.

The breakdown

According to material from the MHLW's "Drink Water for Your Health" campaign (「健康のため水を飲もう」推進運動), an adult man takes in a total of about 2.5 litres of water a day. The breakdown is as follows.

"Drink two litres" may be counting the water in your food twice.

[Verify] The figures are based on the MHLW campaign material (PDF). Check the original text before publication.

Misunderstanding 1｜Drink a fixed amount and you've got it right

How much you need varies with body size, activity, temperature and diet. Japan's Dietary Reference Intakes set no reference value for water intake.

Misunderstanding 2｜Always drink before you feel thirsty

Drinking little and often is recommended, but that does not mean drinking to excess is recommended. The campaign's purpose is to prevent heatstroke, stroke (cerebral infarction) and similar conditions.

Misunderstanding 3｜The more you drink, the healthier you are

Drinking a large amount in a short time can upset the balance of electrolytes in the body. "More is better" is wrong.

Misunderstanding 4｜Counting the volume is the reliable way

Watching the colour of your urine and how you feel is generally described as more practical. Look at your condition rather than counting.

Misunderstanding 5｜The same guide applies to everyone

If you have been given instructions on fluid intake because of kidney disease, heart disease or similar, always follow your doctor's instructions. Your own doctor's instructions come before any general rule.

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Sources

• Ministry of Health, Labour and Welfare (MHLW), "Drink Water for Your Health" campaign [「健康のため水を飲もう」推進運動] (PDF)

https://www.mhlw.go.jp/file/06-Seisakujouhou-10900000-Kenkoukyoku/0000087038.pdf

• MHLW, *Dietary Reference Intakes for Japanese* [日本人の食事摂取基準]

https://www.mhlw.go.jp/stf/seisakunitsuite/bunya/kenkou_iryou/kenkou/eiyou/syokuji_kijyun.html

• Ministry of the Environment, Heat Illness Prevention Information site [熱中症予防情報サイト]

https://www.wbgt.env.go.jp/

⚠️ 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.

This article is not meant to diagnose or manage any specific medical condition. If you are worried about your health, see a doctor rather than relying on your own judgement.

Sources

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