Learn Hardcore Swahili: Mimi sipendi kunywa maji ya bomba usiku. - I do not like to drink tap water at night.

Sipendi kunywa maji ya bomba usiku. – I don’t like to drink tap water at night.
Mimi sipendi kunywa maji ya bomba usiku. – I don’t like to drink tap water at night. (with extra emphasis on I)

You add Mimi mainly for emphasis or contrast, like in English:

I don’t like to drink tap water at night (implying maybe others do).

So the sentence is perfectly correct without Mimi:
Sipendi kunywa maji ya bomba usiku.

What exactly is going on inside the verb sipendi?

Sipendi is made of three parts:

si- = negative prefix for I (1st person singular)
pend = verb root meaning like / love
-i = final vowel used here for the present/habitual negative

So:

ninapenda = I like / I love (affirmative, present/habitual)
- ni- (I) + -na- (present) + pend
  - -a
sipendi = I don’t like (negative, present/habitual)
- si- (I, negative) + pend
  - -i

You do not say si napenda or si penda; the negative is fused into one verb: sipendi.

If sipendi is negative, how would I say the affirmative: "I like to drink tap water at night"?

You keep the rest of the sentence the same and just change sipendi to napenda:

Mimi napenda kunywa maji ya bomba usiku.
= I like to drink tap water at night.

Without Mimi, it’s still clear:

Napenda kunywa maji ya bomba usiku.

Why is it kunywa for "to drink"? What does the ku- mean?

In Swahili, the basic dictionary form of most verbs is the infinitive, formed with:

ku-
- verb root

So:

kunywa = to drink
- ku- (infinitive marker) + nyw (root) + -a

Other examples:

kula = to eat (ku- + l + -a, with a small sound change)
kucheza = to play / dance
kusoma = to read / study

After verbs like penda (to like/love), taka (to want), weza (can), you usually use this ku- infinitive:

Sipendi kunywa. – I don’t like to drink.
Ninataka kunywa maji. – I want to drink water.

You don’t say sipendi nywa; you must keep kunywa here.

Can I say "sipendi ninakunywa maji ya bomba usiku" instead?

No, that doesn’t work in Swahili.

In English you can say "I don’t like to drink…" or "I don’t like drinking…", but in Swahili you do not put a fully conjugated verb (ninakunywa) after penda.

You should use the infinitive:

✅ Sipendi kunywa maji ya bomba usiku. – I don’t like to drink tap water at night.
❌ Sipendi ninakunywa maji ya bomba usiku. – ungrammatical.

What exactly does maji mean? Is it singular or plural?

Maji means water. It is a bit special:

It belongs to noun class 6 (ma- class).
It normally appears only as maji, which is grammatically plural but used like a mass noun in English.

Swahili doesn’t normally use a singular for maji in everyday speech. You just say maji for "water" in general, e.g.:

Nataka maji. – I want (some) water.
Maji ni baridi. – The water is cold.

So even though maji is grammatically plural, you just think of it as "water", not "waters".

Why is it maji ya bomba, not maji la bomba?

The word ya is a possessive/“of” agreement word, and it has to match the class of the first noun, which is maji (class 6).

The pattern is:

[noun] + [agreement form of -a] + [other noun]

For class 6 (ma- nouns like maji), the agreement form is ya.

So:

maji ya bomba = water of the tap → tap water

Compare with other classes:

chai ya rangi – black tea (tea of color)
kitabu cha Kiswahili – Swahili book (class 7 → cha)
mwanafunzi wa shule – pupil of the school (class 1 → wa)

La is the agreement for some class 5 nouns (e.g. tunda la embe – a mango fruit), not for maji. That’s why maji la bomba is wrong.

What does bomba mean exactly here?

In this context, bomba means a tap or faucet (also "pipe" in a general sense).

So:

maji ya bomba = water from the tap → tap water

Other related phrases:

bomba la maji – a water tap
maji ya kisima – well water
maji ya chupa – bottled water

So your sentence is specifically about tap water, not just any water.

Why is there no word like "at" before usiku? Why not katika usiku?

With many time words, Swahili doesn’t need a preposition like "at":

usiku – at night
asubuhi – in the morning
jioni – in the evening
jana – yesterday
leo – today
kesho – tomorrow

So:

Sipendi kunywa maji ya bomba usiku.
= I don’t like to drink tap water at night.

You can say usiku in other ways (e.g. usiku wa manane – midnight), but katika usiku is not the natural way to say at night in this sentence.

Can usiku be moved to the beginning of the sentence?

Yes. Time expressions are quite flexible in Swahili. You can say:

Usiku sipendi kunywa maji ya bomba.
Literally: At night I don’t like to drink tap water.

The meaning is the same; you’re just putting extra emphasis on at night. Both:

Sipendi kunywa maji ya bomba usiku.
Usiku sipendi kunywa maji ya bomba.

are correct.

How would I say "I didn’t like to drink tap water at night" (past tense)?

You change the verb to the negative past form:

Sikupenda kunywa maji ya bomba usiku.

Breakdown:

si- = I (negative)
-ku- = past
pend = like / love
-a (often realized as part of -penda)

So:

Nilipenda kunywa maji ya bomba usiku. – I liked to drink tap water at night.
Sikupenda kunywa maji ya bomba usiku. – I didn’t like to drink tap water at night.

How is kunywa pronounced, especially the nyw part?

Kunywa is pronounced roughly as:

ku-nywa → koo-nywah (in English-like approximation)

Key points:

ny is like the "ny" in "canyon" or the Spanish ñ in "niño".
y is part of that same sound; you don’t say n-y separately.
w is a normal w, and the a is like "a" in "father".

So say it smoothly as two syllables: ku-nywa, not kun-yu-wa or kun-i-wa.