Vannet går gjennom røret.

The ending -et is the definite singular ending for many neuter nouns in Norwegian.

• vann = water
• vannet = the water
• rør = pipe / tube
• røret = the pipe / tube

So Vannet går gjennom røret literally contains the water and the pipe.

Vann is the indefinite form, while vannet is the definite form.

Compare:

• Vann er viktig. = Water is important.
  (water in general)
• Vannet er kaldt. = The water is cold.
  (specific water)

In Vannet går gjennom røret, the sentence is talking about specific water, not water in general.

Because rør is a neuter noun.

In Bokmål, the usual definite singular endings are:

• masculine: -en
• feminine: -a or sometimes -en
• neuter: -et

So:

• en bil → bilen
• ei bok → boka
• et rør → røret

That is why you get røret, not røren.

Yes, går is the present tense of gå, which often means walk or go. But in Norwegian, just like in English, verbs of movement can be used more broadly.

Here går gjennom means something like:

• goes through
• passes through
• runs through
• flows through (depending on context)

So Vannet går gjennom røret is perfectly natural Norwegian, even though water does not literally walk.

Yes, you could. Flyter means flows.

The difference is mainly tone and focus:

• Vannet går gjennom røret = everyday, natural, very common
• Vannet flyter gjennom røret = more explicitly describes the flowing movement

In many contexts, går gjennom sounds more idiomatic and general.

Gjennom means through.

It is a preposition used when something passes from one side of something to the other, or moves inside and across it.

Examples:

• gå gjennom døra = go through the door
• se gjennom vinduet = look through the window
• vannet går gjennom røret = the water goes through the pipe

This is the normal Norwegian main-clause word order:

subject + verb + other elements

So:

• Vannet = subject
• går = verb
• gjennom røret = prepositional phrase

This is the same basic order as English:
The water goes through the pipe.

Yes. Norwegian allows that kind of word order change for emphasis or style.

Gjennom røret går vannet still means the same thing, but now gjennom røret is put first for focus.

When something other than the subject comes first in a main clause, Norwegian still keeps the verb in the second position. That is why it becomes:

• Gjennom røret går vannet not
• Gjennom røret vannet går

It can mean both pipe and tube. The exact translation depends on context.

• plumbing or water system: usually pipe
• laboratory, industrial, or technical context: often tube

So røret could be translated as either the pipe or the tube, depending on what kind of object is meant.

A rough guide for an English speaker is:

VAHN-net

A few points:

• a is more like the a in father than the a in cat
• the tt is pronounced as a clear t
• the final -et is usually unstressed

Pronunciation varies somewhat by dialect, but that rough version is good enough for learners.

A rough guide is:

RUR-et or RER-et, depending on how well you can make the Norwegian ø sound.

The difficult part is ø, which does not exist in standard English. It is somewhat similar to:

• the vowel in French bleu
• or the vowel in German schön

Also:

• the r is usually rolled or tapped more than in most English accents
• the final -et is weak and unstressed

This word is tricky for English speakers.

A rough approximation is:

YEN-nom or YEN-num

Helpful notes:

• gj at the beginning is often pronounced somewhat like y
• the e is short
• the nn is a clear doubled consonant
• the last vowel may sound reduced depending on dialect

It is best to listen to native audio for this word, because spelling and pronunciation are not very transparent here.

Yes, but it means something different.

• Vannet går gjennom røret = The water goes through the pipe
  (specific water, specific pipe)
• Vann går gjennom rør = Water goes through pipes
  (general statement)

So both are grammatical, but they are used in different situations.

This sentence is Bokmål.

Clues include:

• vannet as a common Bokmål definite form
• gjennom is standard in Bokmål

In Nynorsk, you might more often see forms like:

• vatnet
• sometimes different phrasing depending on style

So a learner should treat Vannet går gjennom røret as standard Bokmål.