Sumber air itu bersih.

Sumber air is a noun phrase meaning water source or source of water.

• sumber = source
• air = water

In Indonesian, noun + noun combinations like this are very common, and the first noun is often understood through the second one. So sumber air literally looks like source water, but naturally means water source.

In Indonesian, demonstratives like ini (this) and itu (that/the) usually come after the noun.

So:

• sumber air itu = that water source / the water source

This is different from English, where this/that comes before the noun.

Examples:

• rumah itu = that house / the house
• buku ini = this book

In your sentence, itu refers to the whole noun phrase sumber air, not just air.

It can feel like either one, depending on context.

In many sentences, itu literally means that, but it is also often used to mark something as specific or already known, which can feel like English the.

So sumber air itu bersih could be understood as:

• That water source is clean
• The water source is clean

The exact best translation depends on the situation.

Indonesian often does not use a verb like to be in simple present sentences with adjectives.

So:

• Sumber air itu bersih = The water source is clean

There is no need to add a word for is.

This is very normal in Indonesian:

• Dia tinggi = He/She is tall
• Rumah itu besar = The house is big

Bersih is mainly an adjective, meaning clean.

In this sentence, it works as the predicate:

• Sumber air itu = subject
• bersih = predicate adjective

So the structure is basically:

• [noun phrase] + [adjective]

This is a very common Indonesian sentence pattern.

Normally, no. Adalah is generally not used before adjectives like bersih in ordinary sentences.

Natural:

• Sumber air itu bersih

Unnatural or incorrect in most normal usage:

• Sumber air itu adalah bersih

Adalah is more commonly used:

• in formal definitions
• before nouns or noun phrases, not adjectives

Example:

• Air adalah sumber kehidupan. = Water is a source of life.

Yes — in Indonesian, air means water, not air in the English sense.

Important pronunciation note:

• air in Indonesian is pronounced roughly like ah-eer

If you want to say air as in the atmosphere, the usual Indonesian word is:

• udara = air

So:

• air bersih = clean water
• udara bersih = clean air

This is a very common point of confusion for English speakers.

You use tidak before the adjective:

• Sumber air itu tidak bersih. = The water source is not clean.

This is the normal way to negate adjectives and verbs in Indonesian.

Compare:

• bersih = clean
• tidak bersih = not clean

Yes. That changes itu to ini:

• Sumber air ini bersih. = This water source is clean.
• Sumber air itu bersih. = That water source is clean.

So the structure stays the same; only the demonstrative changes.

Yes, in meaning it is understood as present: The water source is clean.

But Indonesian verbs and predicates usually do not change form for tense the way English does. Tense is often understood from context or shown with time words.

So bersih does not change the way English is/was/will be changes.

If needed, time can be added:

• Sekarang sumber air itu bersih. = Now the water source is clean.
• Dulu sumber air itu bersih. = The water source used to be clean.

By itself, it does not explicitly mark number. It can be understood as singular or plural from context, though in this sentence it will usually be taken as singular because of the context and the presence of itu.

If you really wanted to make plural clear, Indonesian often relies on context or sometimes reduplication:

• sumber-sumber air = water sources

But in everyday use, people often leave number unmarked unless it matters.