Translation guide
In Japanese, the way you say 'boiling water' depends on whether you mean water that is currently boiling, water that has been boiled and is still hot, or simply hot water in general. The most common and useful word is お湯 (oyu), which means hot water, often implying it has been boiled. For water that is actively boiling, use 沸騰したお湯 (futtō shita oyu) or the verb 沸かす (wakasu) to boil water.
The most common way to refer to hot water, such as for tea, cooking, or bathing. This is the default word for 'boiling water' in many contexts where the water is hot but not necessarily bubbling.
This is the standard word for hot water. It implies the water has been heated, usually boiled, and is used for drinking, cooking, bathing, etc. It does not necessarily mean the water is currently boiling.
お湯を沸かしてください。
Please boil some water.
お湯で顔を洗う。
I wash my face with hot water.
Same as お湯 but without the honorific prefix. Used in compounds or more casual/plain contexts. Often seen in public bath signs or product names.
湯加減を見る。
Check the temperature of the bath water.
Water that is currently bubbling and boiling, often at 100°C. Used when you need to emphasize the boiling state.
Literally 'boiled hot water'. 沸騰する means to reach a rolling boil. This phrase clearly indicates the water is at boiling point.
沸騰したお湯にパスタを入れる。
Put the pasta into the boiling water.
Using the progressive form emphasizes the ongoing boiling action. Slightly more descriptive than 沸騰したお湯.
沸騰しているお湯を注ぐ。
Pour the boiling water.
Means 'boiling water' or 'scalding hot water'. Often used in warnings or instructions. Can imply water hot enough to cause burns.
When you want to express the action of making water boil, rather than the water itself.
Transitive verb meaning 'to boil (water)'. Use this when someone is actively boiling water.
お湯を沸かす。
Boil water.
やかんでお湯を沸かした。
I boiled water in a kettle.
Intransitive verb meaning 'to boil' or 'to come to a boil'. Describes the water itself boiling.
お湯が沸いた。
The water has boiled.
Water that was boiled and then cooled, often for drinking or safety.
Specifically means boiled water that has been cooled. Commonly used for baby formula or drinking water.
赤ちゃんに湯冷ましを飲ませる。
Give the baby cooled boiled water.
Descriptive phrase: 'water that has been boiled once'. Used when you need to be clear that the water was boiled and then cooled.
一度沸騰させた水を使ってください。
Please use water that has been boiled once.
水 means cold water. Using 水 to refer to hot or boiling water is incorrect. Always use お湯 for hot water.
沸騰した (futtō shita) specifically means 'boiling' (at 100°C). 熱い (atsui) just means 'hot'. You can have hot water that is not boiling, so be precise if the boiling state matters.
お茶にお湯が必要です。
I need boiling water for the tea.
Natural Japanese uses お湯, not a literal translation of 'boiling water'.
お湯が沸騰しています。
The water is boiling.
熱湯注意。
Caution: boiling water.