atui hi ha, nettyuusyou ni naranai you ni, komame ni mizu wo nonde kudasai.

It can naturally mean all of those, depending on context.

In this sentence, 暑い日は is best understood as:

• on hot days
• when it’s hot

Breakdown:

• 暑い = hot
• 日 = day
• 暑い日 = a hot day / hot days
• は = topic marker

So 暑い日は means something like as for hot days... or when it is a hot day..., which sounds more natural in English as on hot days.

Because 暑い is directly modifying 日.

In Japanese, i-adjectives can go directly before nouns:

• 暑い日 = hot day
• 寒い日 = cold day
• 長い道 = long road

So this is just like English adjective + noun.

は marks the topic.

Here, it sets the situation or context: as for hot days.

The sentence is then telling you what to do in that situation:

• 暑い日は、...飲んでください。
• On hot days, please drink water...

So は is not the subject marker here; it is introducing the topic or condition under which the advice applies.

Because the verb なる often takes に to mark what something becomes.

Examples:

• 医者になる = become a doctor
• 元気になる = become well
• 静かになる = become quiet
• 熱中症になる = get heatstroke / become affected by heatstroke

So:

• 熱中症に = into the state of heatstroke
• ならない = do not become

Together: 熱中症にならない = not get heatstroke

Here, 〜ように means so that... or in order to...

So:

• 熱中症にならないように = so that you do not get heatstroke
• more naturally: to avoid heatstroke

This pattern is very common:

• 忘れないようにメモします。 = I’ll make a note so that I don’t forget.
• 遅れないように早く出ます。 = I’ll leave early so that I’m not late.

In your sentence, it introduces the purpose of drinking water.

Because the pattern uses the plain form of the verb before ように.

For a negative verb, that plain form is:

• なる → ならない

So:

• 熱中症になるように = so that one gets heatstroke
• 熱中症にならないように = so that one does not get heatstroke

You do not use the -なく form here.

Both can express purpose, but they are not always interchangeable.

〜ように is often used when the goal is:

• something you try to make happen
• something not fully under direct control
• something stated as a desired outcome

Here, not getting heatstroke is the outcome you want to avoid, so 〜ように fits very naturally.

So:

• 熱中症にならないように、水を飲んでください。
• Please drink water so that you don’t get heatstroke.

Using ために here is less natural. 〜ために often feels more like a direct purpose tied to intentional action, while 〜ように is very common in advice or prevention sentences like this.

こまめに means frequently, regularly, or in small, careful intervals.

In this sentence, it suggests:

• don’t wait too long between drinks
• drink water little by little, often
• keep hydrating regularly

So こまめに水を飲む means something like:

• drink water frequently
• sip water regularly

It is not just a lot of water; it emphasizes often.

Because こまめ behaves like a na-adjective, and when a na-adjective is used adverbially, it often takes に.

Compare:

• 静かな人 = a quiet person
• 静かに話す = speak quietly

Similarly:

• こまめな人 = a diligent / attentive person
• こまめに飲む = drink frequently / attentively / regularly

So こまめに is the adverb form.

Because 〜てください makes it a request or instruction:

• 飲む = drink
• 飲んで = te-form of drink
• 飲んでください = please drink

So the full sentence is giving advice politely:

• Please drink water frequently...

This is a very common form for instructions, announcements, and health/safety guidance.

No. The phrase こまめに makes it clear that the idea is drink water regularly, not all at once.

So the overall nuance is:

• Keep drinking water in small amounts throughout the day
• Hydrate often

That is why こまめに is important in the sentence.

Japanese often omits the subject when it is clear from context.

In this kind of sentence, the implied subject is usually you:

• (あなたが) 熱中症にならないように、こまめに水を飲んでください。
• Please drink water regularly so that you don’t get heatstroke.

Because it is advice directed at the listener, Japanese does not need to say あなた.

A good way to parse it is:

1. 暑い日は、
   On hot days,

2. 熱中症にならないように、
   so that you don’t get heatstroke / to avoid heatstroke,

3. こまめに水を飲んでください。
   please drink water regularly.

So the whole structure is:

[time/situation] + [purpose/prevention] + [main request]

That structure is very common in Japanese advice sentences.

Literally, 熱中症 refers to a heat-related medical condition caused by heat. In everyday English, heatstroke is the most natural translation in many contexts, especially in safety warnings.

However, depending on the context, it can also be understood more broadly as heat illness or heat-related illness.

In a sentence like this, English usually says:

• to avoid heatstroke
• to prevent heat-related illness

But heatstroke is the most common simple translation for learners.

The commas help separate the sentence into easy-to-read chunks:

• 暑い日は、
• 熱中症にならないように、
• こまめに水を飲んでください。

They are not absolutely required in every case, but they are very natural here because the sentence has:

• a topic phrase
• a purpose phrase
• the main instruction

Japanese commas often guide the reader through the structure rather than matching English punctuation exactly.