Vannskålen brukes under tilvenningsperioden.

Because Norwegian usually writes compound nouns as a single word.

• vann = water
• skål = bowl

So:

• vannskål = water bowl
• vannskålen = the water bowl

This is very normal in Norwegian. English often uses two words where Norwegian prefers one compound word.

The ending -en is the definite singular ending, meaning the.

So:

• en vannskål = a water bowl
• vannskålen = the water bowl

The noun takes its gender from the last part of the compound, here skål, which is a common-gender noun: en skål.

Brukes is the present passive form of å bruke = to use.

So brukes means is used or gets used, depending on context.

Compare:

• Vannskålen bruker ... → this would be wrong here, because it would mean something like the water bowl uses...
• Vannskålen brukes ... = the water bowl is used...

In this sentence, Norwegian uses the -s passive, which is common in instructions and formal writing.

This kind of passive sentence is very common in Norwegian instructions, manuals, and informational text.

Vannskålen brukes under tilvenningsperioden sounds neutral and practical, like:

• The water bowl is used during the acclimatization period

An active version is possible, but it would need a subject:

• Man bruker vannskålen under tilvenningsperioden = One uses the water bowl during the acclimatization period

The passive is often preferred when the doer is unimportant or obvious.

Tilvenningsperioden is another compound noun.

It can be broken down like this:

• tilvenning = acclimatization, adjustment, getting used to something
• perioden = the period

So tilvenningsperioden means the acclimatization period or the adjustment period.

A useful related verb is:

• å tilvenne seg = to get used to, to acclimatize oneself

So the noun tilvenning is the process of getting used to something.

Because it refers to a specific period, not just any period.

Compare:

• en tilvenningsperiode = an acclimatization period
• tilvenningsperioden = the acclimatization period

In Norwegian, the idea of the is usually added at the end of the noun, not as a separate word in front.

So there is no separate word for the before tilvenningsperioden because it is already built into -en.

Here, under means during, not physically beneath.

So:

• under tilvenningsperioden = during the acclimatization period

This is the same kind of usage as in English when we say:

• under the summer
• under the meeting

though in natural English, during is often more common.

Yes. You can move the time phrase to the front:

• Under tilvenningsperioden brukes vannskålen.

This still means the same thing.

But Norwegian has a verb-second rule in main clauses, so when under tilvenningsperioden comes first, the verb brukes must stay in second position.

That is why you get:

• Under tilvenningsperioden brukes vannskålen.

and not:

• Under tilvenningsperioden vannskålen brukes.

Yes. Norwegian also often uses bli + past participle to make a passive meaning.

So another possible version is:

• Vannskålen blir brukt under tilvenningsperioden.

This also means The water bowl is used during the acclimatization period.

Very roughly:

• brukes = shorter, often more formal or written
• blir brukt = very common, often a bit more conversational or explicit

Both are correct.