Learn Hardcore Finnish: Puoliaika on hyvä hetki juoda vettä. - Halftime is a good moment to drink water.

In sports, it means the half-time break in games like football (soccer), basketball, etc.
You wouldn’t use puoliaika for a theater or concert break. There you’d say väliaika (intermission).

So in this sentence, Puoliaika on hyvä hetki juoda vettä, the context is almost certainly a sports game.

Why is there no word for “the” in Puoliaika on hyvä hetki juoda vettä?

Finnish has no articles at all — no “a”, “an”, or “the”.

Whether you mean:

“Halftime is a good moment to drink water.”
or “The halftime is a good moment to drink water.”

you still say: Puoliaika on hyvä hetki juoda vettä.

The exact nuance (a/the) comes from context, not from a separate word.

Why are puoliaika and hyvä hetki both in the basic form (no endings)?

This is a typical “X is Y” structure:

Puoliaika = subject (nominative)
on = “is”
hyvä hetki = predicative (also nominative)

In Finnish, when you say “X is Y”, both X and Y usually appear in the nominative singular (basic dictionary form):

Puoliaika on hyvä hetki. – Halftime is a good moment.
Tämä kirja on mielenkiintoinen. – This book is interesting.
Kahvi on kuumaa. – The coffee is hot.

So hyvä hetki is not in the object case; it’s describing what puoliaika is.

What’s the difference between hetki and aika? Could I say hyvä aika instead of hyvä hetki?

Both are possible, but they feel slightly different:

hetki = a moment, a relatively short point in time
aika = time in a more general or longer sense

In this sentence:

hyvä hetki emphasizes a brief period / moment, like the actual half-time break.
hyvä aika would be more like “a good time (in general)”, slightly less precise, but still correct.

So:

Puoliaika on hyvä hetki juoda vettä. – very natural, focusing on that specific short break.
Puoliaika on hyvä aika juoda vettä. – also acceptable, just a bit more general-sounding.

Why is the verb on used without a pronoun? Why not Se on hyvä hetki…?

In Finnish you don’t need a subject pronoun when the subject is already present:

Puoliaika on hyvä hetki…
Subject = Puoliaika, so no pronoun is needed.

Using se here:

Se on hyvä hetki juoda vettä.
would normally refer back to something already known:
“That (time/thing) is a good moment to drink water.”

So:

Puoliaika on hyvä hetki… states a general fact about halftime.
Se on hyvä hetki… would be used only if “that” has just been mentioned in the conversation or text.

Why is juoda (to drink) in this exact form? Why not juominen or juomaan?

juoda here is the 1st infinitive, the basic dictionary form used like English “to drink”.

Pattern:

on hyvä hetki + (1st infinitive)
→ on hyvä hetki juoda vettä = is a good moment to drink water

Alternatives:

juominen (the -minen form)
- Juominen on tärkeää. – Drinking is important.
  This behaves like a noun (“drinking” as an activity), not like “to drink” after “good moment to”.
juomaan (illative of the 3rd infinitive)
Often expresses purpose, typically after a motion verb:
- Menen juomaan vettä. – I’m going to drink water.
- Tulen syömään. – I’m coming to eat.

Saying:

Puoliaika on hyvä hetki juomaan vettä
sounds odd in standard Finnish. The normal structure after hetki is the 1st infinitive:
hyvä hetki juoda vettä.

Why is it vettä and not vesi? What does that -ä ending mean?

Vettä is the partitive singular of vesi (water).

Basic pattern with drinking:

juoda + partitive for an unspecified amount of a substance:
- juoda vettä – to drink (some) water
- juoda maitoa – to drink (some) milk
- juoda kahvia – to drink (some) coffee

Reasons for the partitive here:

Uncountable / mass noun: water is not being counted; it’s just “water” in general.
Amount is not specified or completed: not “all the water”, just some.

Compare:

Juon veden. – I drink the water (all of it). (accusative; a specific, complete quantity)
Juon vettä. – I drink (some) water. (partitive; general amount)

So juoda vettä naturally means “to drink water (in general / some water)”, which fits this sentence.

Can I change the word order, like On hyvä hetki juoda vettä puoliaikana?

You can change word order in Finnish, but you must be careful with what sounds natural and what is emphasized.

Original:

Puoliaika on hyvä hetki juoda vettä.
Neutral, natural: subject (Puoliaika) first, then on hyvä hetki juoda vettä as a comment about it.

Other possibilities:

On hyvä hetki juoda vettä puoliaikana.
- Grammatically possible, but more marked and less natural.
- Feels like you’re first talking about “it is a good moment to drink water” in general, and then you add “during halftime” almost as an afterthought.
Hyvä hetki juoda vettä on puoliaika.
- Also grammatically correct, but this emphasizes puoliaika as the good moment.
- Closer to: “The good moment to drink water is halftime.”

For a neutral, typical sentence, Puoliaika on hyvä hetki juoda vettä is the best choice.

Can I use other verbs or objects in the same pattern as on hyvä hetki juoda vettä?

Yes. The pattern is very reusable:

[Noun] on hyvä hetki [1st infinitive] [partitive object].

Examples:

Aamu on hyvä hetki juoda kahvia.
Morning is a good moment to drink coffee.
Ilta on hyvä hetki lukea kirjaa.
Evening is a good moment to read a book.
(kirjaa = partitive of kirja)
Tauko on hyvä hetki syödä jotain.
A break is a good moment to eat something.

The idea is:

on hyvä hetki
- basic infinitive (juoda, lukea, syödä, etc.)
and often a partitive object for an unspecified amount or incomplete action.