Pakningen er viktig for vanntettheten.

In a technical sentence like this, pakning usually means a gasket, seal, or sealing ring—a part that helps prevent leaks.

So here it probably does not mean package or packaging. The context is important:

• everyday context: pakking = packing, what you pack
• technical/mechanical context: pakning = gasket/seal

Because -en is the definite singular ending for many nouns in Bokmål.

• en pakning = a gasket / a seal
• pakningen = the gasket / the seal

So Norwegian often puts the at the end of the noun instead of using a separate word before it.

Because Norwegian usually marks definiteness by adding an ending to the noun itself.

Here:

• pakningen already means the gasket
• vanntettheten already means the watertightness

So a separate article is not needed.

Er is the present tense of å være, which means to be.

So:

• er = is / are
• Pakningen er viktig = The gasket is important

Because the subject is singular, and after er the adjective stays in the singular form here.

• pakningen er viktig = singular
• pakningene er viktige = plural

So viktige would normally be used with a plural subject here.

Here for means for in the sense of important for or important to the functioning of.

The phrase viktig for is very common in Norwegian:

• viktig for helsen = important for health
• viktig for resultatet = important for the result

So viktig for vanntettheten means that the gasket matters to the watertightness.

Because viktig normally goes with for in this kind of meaning.

You learn it as a common combination:

• viktig for noe = important for something

Using til here would sound unnatural in standard Norwegian.

It is built in stages:

• vann = water
• tett = tight
• vanntett = watertight / waterproof
• vanntetthet = watertightness / waterproofness
• vanntettheten = the watertightness / the waterproofness

So it is a derived noun based on the adjective vanntett.

Because Norwegian often creates long compound or derived words.

Here the word keeps the tt from vanntett, and then adds the noun ending:

• vanntett
  • het → vanntetthet
• vanntetthet
  • -en → vanntettheten

Long words like this are very normal in Norwegian, especially in technical language.

Because the sentence is talking about a specific property of a specific object, not watertightness in general.

Compare:

• vanntetthet = watertightness in general
• vanntettheten = the watertightness of this item/system

So the definite form makes it sound more specific and concrete.

Yes. It follows a very standard Norwegian sentence pattern:

• Pakningen = subject
• er = verb
• viktig for vanntettheten = description of the subject

So the structure is basically the same as in English:

• The gasket is important for the watertightness