Lantai kamar mandi harus kedap air.

Indonesian noun phrases usually put the main noun first and the word that describes or narrows it afterward.

So:

• lantai = floor
• kamar mandi = bathroom

lantai kamar mandi literally means floor of the bathroom, which is the natural Indonesian way to say bathroom floor.

This is different from English, where the describing noun often comes first.

Yes. Literally:

• kamar = room
• mandi = bathe / bathing

So kamar mandi is literally bathing room, but in normal usage it means bathroom. In Indonesian, it can also refer to a room with a toilet, so its use can be a bit broader than the English word depending on context.

Indonesian does not normally use articles like the or a/an the way English does.

So lantai kamar mandi can mean:

• the bathroom floor
• a bathroom floor

Which one is meant depends on context. In this sentence, English would usually translate it as the bathroom floor, but Indonesian does not need a separate word for that.

Harus means must, has to, or need(s) to.

In this sentence, it expresses necessity or requirement:

• Lantai kamar mandi harus kedap air.
• The bathroom floor must be waterproof.

It is a very common word for obligation or necessity.

Yes, from an English perspective, you can think of it that way.

Indonesian often does not use a verb like to be when the predicate is an adjective or noun phrase.

So:

• kedap air = waterproof / watertight

And:

• harus kedap air literally feels like must waterproof
• but in natural English it becomes must be waterproof

So there is no separate word for be here, and that is normal Indonesian grammar.

Kedap air means watertight, waterproof, or impermeable to water.

It is made up of:

• kedap = sealed, not letting something through
• air = water

So kedap air literally means something like sealed against water.

In this sentence, it describes the floor as something that should not let water seep through.

Not exactly.

Both can be translated as waterproof in some contexts, but there is a nuance:

• kedap air = watertight, water cannot pass through
• tahan air = water-resistant, able to withstand water

So for a bathroom floor, kedap air is especially appropriate because the idea is that water should not seep through the surface.

It is normally written as two words:

• kedap air

This is a common adjective phrase in Indonesian, where the second word specifies what something is resistant or sealed against.

Compare similar patterns such as:

• tahan panas = heat-resistant
• tahan air = water-resistant

Yes, but it means something slightly different.

• lantai kamar mandi = the bathroom floor
• lantai di kamar mandi = the floor in the bathroom

These can refer to the same thing in many situations, but lantai kamar mandi sounds more like a set noun phrase, while lantai di kamar mandi is a more descriptive phrase.

For this sentence, lantai kamar mandi is the more natural choice.

Indonesian usually shows this kind of relationship just by putting nouns next to each other.

So:

• lantai kamar mandi = bathroom floor / floor of the bathroom

There is no need for a word like of or an ending like ’s. The relationship is understood from word order.

Here, kedap air functions as an adjective phrase describing the floor.

The structure is:

• Lantai kamar mandi = subject
• harus = modal / necessity marker
• kedap air = adjective phrase

So the sentence pattern is basically:

• subject + must + adjective

even though Indonesian does not need a separate word for be.

A more formal or explicit version could be:

• Lantai kamar mandi harus bersifat kedap air.

Here:

• bersifat = to have the character/nature of

This sounds more formal and technical. But the original sentence, Lantai kamar mandi harus kedap air, is already completely correct and natural.

No. Indonesian air means water, and it is pronounced differently from English air.

It is usually pronounced roughly like ah-eer in two syllables.

So:

• air (water) ≠ English air

This is a very common beginner confusion because the spelling looks familiar to English speakers.