Wasser schadet der Fahrradkette.

Because schaden takes the dative case, not the accusative.

• The base form is die Fahrradkette in the nominative.
• In the dative singular, die changes to der.

So:

• die Fahrradkette = the bicycle chain
• der Fahrradkette = to the bicycle chain / for the bicycle chain

In this sentence, Wasser is the subject, and der Fahrradkette is the dative object.

Yes, schaden is a verb that normally takes a dative object.

Examples:

• Das schadet mir. = That is harmful to me.
• Rauchen schadet der Gesundheit. = Smoking harms health.
• Wasser schadet der Fahrradkette. = Water harms the bicycle chain.

This is something English speakers often have to memorize, because English harm or damage does not show case in the same way.

Because Wasser is being used in a general sense, like a substance or material.

German often leaves out the article with mass nouns when speaking generally:

• Wasser ist kalt. = Water is cold.
• Milch ist gesund. = Milk is healthy.
• Wasser schadet der Fahrradkette. = Water harms the bicycle chain.

If you wanted to refer to some specific water, you could use an article, but here the sentence means water in general.

There are two main clues:

1. Verb agreement
   The verb is schadet, which is third person singular.
   Wasser is singular, so it fits as the subject.

2. Case marking
   der Fahrradkette is clearly dative, so it is not the subject here.
   That leaves Wasser as the nominative subject.

So the structure is:

• Wasser = subject
• schadet = verb
• der Fahrradkette = dative object

The dictionary form is schaden.

Here is the pattern:

• ich schade
• du schadest
• er/sie/es schadet
• wir schaden
• ihr schadet
• sie/Sie schaden

So schadet is the form used with er, sie, es, or a singular noun like Wasser.

It is a compound noun, which is very common in German:

• Fahrrad = bicycle
• Kette = chain

Together:

• die Fahrradkette = bicycle chain

In German, the last part of a compound determines the grammatical gender.
Since die Kette is feminine, die Fahrradkette is also feminine.

Yes. The sentence follows normal German main-clause word order:

• Wasser = first position
• schadet = second position
• der Fahrradkette = after the verb

This is the standard verb-second pattern.

You could also say:

• Der Fahrradkette schadet Wasser.

That is still grammatically correct, but it sounds more marked or stylistic, because now the dative phrase is in first position. The verb still stays in second position.

Not exactly.

• schaden usually means to harm, to be harmful to, or to cause damage to
• beschädigen means to damage in a more direct, concrete sense

Compare:

• Wasser schadet der Fahrradkette.
  = Water is harmful to the bicycle chain / Water damages the bicycle chain.

• Das hat die Fahrradkette beschädigt.
  = That damaged the bicycle chain.

Also, beschädigen takes the accusative, while schaden takes the dative.

It is singular because the sentence is talking about the bicycle chain as a general item.

Yes, it could be plural:

• Wasser schadet den Fahrradketten. = Water harms the bicycle chains.

Notice the dative plural:

• die Fahrradketten = nominative plural
• den Fahrradketten = dative plural

So the article changes again in the plural.

Depending on context, natural English versions could be:

• Water harms the bicycle chain.
• Water is bad for the bicycle chain.
• Water damages the bicycle chain.
• Water can damage a bicycle chain.

A learner should note that German often uses schaden where English might prefer be bad for or damage, depending on context.

A simple pronunciation guide is:

• Wasser ≈ VAH-ser
• schadet ≈ SHAH-det
• der Fahrradkette ≈ dair FAHR-raht-ket-uh

A few helpful points:

• w in German sounds like English v
• sch sounds like English sh
• z in Fahrrad is not present, so there is no ts sound there
• the final -e in Kette is pronounced like a soft uh

A rough full version:

• VAH-ser SHAH-det dair FAHR-raht-ket-uh