La regadera contiene agua para el perejil.

Here, regadera most likely means watering can.

A useful warning: in some parts of Latin America, especially Mexico, regadera can also mean shower or showerhead. But in this sentence, because of para el perejil, the gardening meaning is the one that makes sense.

So the context tells you it is something holding water for a plant.

Because regadera is a feminine noun, so it takes la in the singular.

• la regadera = the watering can
• una regadera = a watering can

Like many nouns ending in -a, it is feminine, though that is a pattern, not an absolute rule.

Contiene is the third-person singular present tense of contener.

That means it matches la regadera, which is a singular subject:

• la regadera contiene = the watering can contains

A few present-tense forms of contener are:

• yo contengo
• tú contienes
• él/ella/usted contiene
• nosotros contenemos
• ellos/ellas/ustedes contienen

It behaves a lot like tener, with a stem change in some forms.

Both are possible, but they are not exactly the same in tone.

• contiene = contains
• tiene = has

So:

• La regadera contiene agua... sounds a little more precise or formal.
• La regadera tiene agua... sounds more everyday and conversational.

In normal speech, many speakers would probably say tiene.

Because agua is being used as a mass noun here, not as a specific, identified thing.

So contiene agua means contains water, just like English often says contains water rather than contains the water.

If you wanted to refer to specific water, you could use an article:

• La regadera contiene el agua que necesitamos.

Also, remember that when agua does take a singular definite article, it is usually el agua, not la agua, because of pronunciation:

• el agua fría

But the noun is still feminine, which is why the adjective is fría, not frío.

Para here shows purpose or intended use.

So agua para el perejil means:

• water for the parsley
• water intended for the parsley
• water to use on the parsley

It does not mean the water belongs to the parsley. It means the water is meant to help or be used on it.

Spanish often uses the definite article more than English does.

Here, el perejil can mean:

• a specific parsley plant already understood from the context, or
• parsley as the relevant plant being talked about

So para el perejil sounds natural.

If you remove the article, para perejil would sound unnatural in this sentence.

Yes. That idea is understood from the context.

The sentence literally mentions water for the parsley, and the listener naturally understands that the water is for watering the parsley.

If you want to make that action explicit, you could say:

• La regadera contiene agua para regar el perejil.

That is more explicit, but the original sentence is still understandable.

It is grammatical and clear, but contiene sounds a bit more formal or written than everyday speech.

In casual conversation, many speakers would be more likely to say:

• La regadera tiene agua para el perejil.

And if they want to be extra clear about the purpose:

• La regadera tiene agua para regar el perejil.

So the original sentence is correct, but not the most casual everyday wording.

Yes. This is a good vocabulary note for learners.

Depending on the country or region, regadera can refer to:

• a watering can
• a sprinkler
• a shower or showerhead

That is why context matters so much. In this sentence, the mention of perejil makes the gardening meaning the obvious one.