Гидроизоляция защищает инженерные коммуникации.

Защищает is the 3rd person singular present tense of the imperfective verb защищать.

In Russian, the present tense of an imperfective verb can mean:

• a general fact: protects
• a repeated action: protects regularly
• an action happening now, depending on context: is protecting

In this sentence, it sounds like a general statement about what waterproofing does, so protects is the most natural translation.

The dictionary form is защищать — to protect.

This is an imperfective verb, which is used for:

• ongoing actions
• repeated actions
• general descriptions

Its perfective partner is защитить, which means something like to protect successfully / to protect completely and is used for a completed result.

So:

• Гидроизоляция защищает... = waterproofing protects...
• Гидроизоляция защитит... = waterproofing will protect...

Because it is in the nominative case, which is the usual case for the subject.

The sentence structure is:

• Гидроизоляция = subject
• защищает = verb
• инженерные коммуникации = direct object

So the basic meaning is:

Waterproofing protects engineering utilities / service systems.

It is in the accusative plural, because it is the direct object of защищает.

The verb защищать takes a direct object in the accusative:

• защищать что? = to protect what?

So:

• защищает инженерные коммуникации

A useful detail: with inanimate plural nouns, the accusative form is the same as the nominative form. That is why инженерные коммуникации looks the same as the dictionary-style plural form.

Because it is a plural adjective agreeing with коммуникации.

Russian adjectives must agree with the noun in:

• gender
• number
• case

Here:

• коммуникации is plural
• the phrase is accusative plural
• for inanimate plural nouns, accusative looks like nominative

So the adjective takes the plural form инженерные.

Not in the everyday English sense.

In technical, architectural, and construction contexts, коммуникации often means:

• utilities
• service lines
• engineering networks
• building systems

For example, it can refer to:

• water pipes
• sewage
• heating
• ventilation
• cables
• other infrastructure systems

So инженерные коммуникации is a set technical phrase meaning something like:

• engineering utilities
• building service systems
• utility lines

This is a very common false-friend type issue for English speakers.

In this technical meaning, Russian often uses коммуникации in the plural, because it refers to a whole set of systems or networks rather than one single line.

So инженерные коммуникации usually means the collection of building or infrastructure systems.

A singular form коммуникация exists, but in this context the plural is much more natural.

Yes, гидроизоляция is a feminine singular noun, because it ends in -я.

However, in the present tense, Russian verbs do not show gender. They only show person and number.

So защищает is singular because the subject is singular, but it does not specifically show that the subject is feminine.

Gender would matter in the past tense:

• Гидроизоляция защищала... = waterproofing protected...

There, защищала is feminine singular.

Russian has no articles.

So a sentence like this can mean:

• Waterproofing protects engineering utilities
• The waterproofing protects the engineering utilities
• A waterproofing layer protects engineering utilities

The exact choice in English depends on context.

Russian usually expresses definiteness through:

• context
• word order
• intonation
• sometimes additional words, if needed

Yes. Russian word order is more flexible than English word order because case endings show who is doing what.

The neutral order here is:

Гидроизоляция защищает инженерные коммуникации.

But you could also say:

Инженерные коммуникации защищает гидроизоляция.

That still means Waterproofing protects engineering utilities, but it gives a different emphasis, roughly highlighting engineering utilities first.

So the basic roles stay clear because of grammar, not just position.

A helpful stressed version is:

Гидроизоля́ция защища́ет инжене́рные коммуника́ции.

Approximate pronunciation:

• гидроизоля́ция = gee-dro-ee-za-LYA-tsi-ya
• защища́ет = za-shchee-SHA-yet
• инжене́рные = een-zhe-NER-ny-ye
• коммуника́ции = ka-moo-nee-KA-tsi-ee

A rough full transliteration: Gidroizolyatsiya zashchishchayet inzhenernye kommunikatsii.

Most naturally, it states a general fact.

Russian often uses the imperfective present tense for:

• definitions
• technical descriptions
• general truths
• standard functions of something

So this sounds like the kind of sentence you might see in:

• a manual
• a construction guide
• a technical description
• product information

It means that waterproofing, in general, serves to protect engineering utilities.