samui asa wa oyu o nomimasu.

On cold mornings, I drink hot water.

Breakdown of samui asa wa oyu o nomimasu.

• は: topic particle
• を: direct object particle
• 飲のむ: to drink
• 寒さむい: cold

Questions & Answers about samui asa wa oyu o nomimasu.

Why is it 寒い朝 and not 寒いの朝 or 寒く朝?

Because 寒い is an i-adjective, and i-adjectives can directly modify a noun.

• 寒い朝 = a cold morning / cold mornings

You do not need の here.
You also do not change 寒い to 寒く when it directly modifies a noun.

Compare:

• 寒い朝 = a cold morning
• 朝が寒い = the morning is cold
• 寒くなる = become cold

So in this sentence, 寒い is simply describing 朝.

What does は mean after 朝 here?

Here, は marks 寒い朝 as the topic.

So the sentence is talking about cold mornings as the context:

• 寒い朝は、お湯を飲みます。
• As for cold mornings, (I) drink hot water.

This is slightly different from just marking the subject.
It gives a feeling like:

• When it’s a cold morning...
• On cold mornings...
• As for cold mornings...

Japanese often uses は to set the scene or establish what the statement is about.

Why is there no word for in the sentence?