Tunachohitaji sasa ni maji safi.

It is made of several pieces:

• tu- = we
• -na- = present tense
• -cho- = a relative marker meaning something like what / that which
• hitaji = need

So tunachohitaji means what we need or more literally that which we need.

This is very typical Swahili: a lot of meaning is packed into one verb form.

-cho- is the relative marker for noun class 7.

In this sentence, the idea is the thing that we need. The word thing is understood rather than stated openly, and thing in Swahili is often kitu, which belongs to class 7. Because of that, the relative marker is -cho-.

So:

• tunachohitaji = the thing that we need / what we need

Yes, you can think of it that way.

A fuller version could be:

• Kile tunachohitaji sasa ni maji safi.

That would mean something like The thing that we need now is clean water.

In normal Swahili, the head word is often left out when it is obvious, so tunachohitaji by itself naturally means what we need.

You can say tunahitaji, but it gives a different structure.

• Tunahitaji maji safi sasa. = We need clean water now.
• Tunachohitaji sasa ni maji safi. = What we need now is clean water.

The second version is more focused or emphatic. It highlights what we need now, and then identifies it as clean water.

So the difference is mainly one of sentence structure and emphasis, not basic meaning.

Ni links two noun phrases, like is / are in English.

Here it connects:

• tunachohitaji sasa = what we need now
• maji safi = clean water

So ni is the word that makes the sentence mean X is Y.

In simple identifying sentences like this, Swahili commonly uses ni.

Great question. Maji belongs to noun class 6, which often has plural-looking forms, but maji is usually treated as a mass noun meaning water.

So even though it looks plural from a noun-class point of view, in English it is usually translated simply as water, not waters.

This is normal in Swahili. Some nouns do not match English ideas of singular and plural in a simple way.

Because in Swahili, adjectives usually come after the noun.

So:

• maji safi = clean water
• literally: water clean

That noun + adjective order is very common in Swahili.

Some Swahili adjectives change to agree with the noun class, but safi is commonly used in a form that stays the same.

So you can have:

• maji safi = clean water
• nguo safi = clean clothes / clean clothing
• hewa safi = clean air

So even though maji belongs to a certain noun class, safi does not visibly change here.

Here sasa means now, and it goes with tunachohitaji:

• tunachohitaji sasa = what we need now

So the idea is not just what we need, but what we need now, at this moment.

Yes, it often can.

For example:

• Sasa tunachohitaji ni maji safi.
• Tunachohitaji sasa ni maji safi.

Both are natural. The main meaning stays the same, but the focus or rhythm changes a little.

• Sasa tunachohitaji... can feel like Now, what we need...
• Tunachohitaji sasa... keeps now closely tied to what we need

Not exactly. Swahili does not need a separate standalone word here in the same way English uses what.

Instead, Swahili builds the idea into the verb form through the relative marker:

• tu-na-cho-hitaji

So English uses a separate word, what, but Swahili expresses that meaning inside the verb itself. That is why one Swahili word can correspond to several English words.