Learn Hardcore Danish: Jeg ville drikke vand, hvis jeg var tørstig.

Jeg vil drikke vand = I want to / I will drink water (real intention or future)
Jeg ville drikke vand, hvis jeg var tørstig = I would drink water, if I were thirsty (hypothetical, not real)

So ville is used because the sentence is not about what actually is the case, but about what would happen if something were true.

But isn’t ville technically past tense? How can it talk about a hypothetical present?

Yes, ville is morphologically the past tense of vil, but in Danish (as in English and German), past forms of modal verbs are also used for unreal / hypothetical situations, not only for real past time.

Compare:

Real present/future:
- Hvis jeg er tørstig, vil jeg drikke vand.
  If I am thirsty, I will drink water.
Unreal (contrary-to-fact) present:
- Hvis jeg var tørstig, ville jeg drikke vand.
  If I were thirsty, I would drink water.

So the “past” form ville here signals irreality/hypothesis, not past time.

Can I also say “Hvis jeg var tørstig, ville jeg drikke vand”? Is there any difference?

Yes, that is completely correct, and very common:

Hvis jeg var tørstig, ville jeg drikke vand.
Jeg ville drikke vand, hvis jeg var tørstig.

Meaning and nuance are essentially the same. The only difference is which part you emphasize first:

Starting with Hvis jeg var tørstig… slightly highlights the condition.
Starting with Jeg ville drikke vand… slightly highlights the result.

Grammatically, both word orders are fine. Just remember in Danish that in a main clause the verb must be in second position, which both versions respect:

Jeg (1) ville (2) drikke vand …
Hvis jeg var tørstig, ville (1) jeg (2) drikke vand …

Why is it var (past) and not er (present) in hvis jeg var tørstig?

The choice between er and var after hvis changes the meaning:

Hvis jeg er tørstig, drikker jeg vand.
If I am (actually / possibly) thirsty, I drink water.
→ A real, possible situation (open condition).
Hvis jeg var tørstig, ville jeg drikke vand.
If I were thirsty, I would drink water.
→ A hypothetical, unreal situation (you are implying you’re not thirsty).

So var here is not “past time” but a past form used for an unreal present, similar to English “if I were” instead of “if I am” in counterfactual sentences.

Why is it tørstig and not tørst? Aren’t they both “thirsty”?

They are related, but not the same:

tørstig = adjective = “thirsty”
- Jeg er tørstig. = I am thirsty.
tørst = noun = “thirst”
- Han døde af tørst. = He died of thirst.
- Jeg har tørst is possible but not common in everyday speech; jeg er tørstig is the normal way.

In hvis jeg var tørstig, you need an adjective after være (to be), so tørstig is the correct form.

Why is there a comma before hvis? Could I leave it out?

Hvis jeg var tørstig is a subordinate clause (a dependent clause), and in traditional Danish comma rules you always put a comma before subordinate clauses, so:

Jeg ville drikke vand, hvis jeg var tørstig.

Under the newer, more relaxed comma rules, you may leave out some commas before subordinate clauses, so you might also see:

Jeg ville drikke vand hvis jeg var tørstig.

Many Danes still use the comma in this case, and for learners it is generally safer to include it before hvis-clauses.

Why is there no article before vand? Why not noget vand or et vand?

Vand is usually treated as a mass / uncountable noun when you talk about drinking water in general:

Jeg drikker vand. = I drink water.

Using noget vand (some water) is also correct, but a bit more specific or slightly more “measured”:

Jeg ville drikke noget vand. = I would drink some water.

Et vand normally means a (bottle / glass of) water in some contexts, especially in cafés or bars:

Jeg vil gerne have et vand. = I’d like a water (a bottle / glass of water).

In your sentence, plain “vand” is the most neutral and natural.

What’s the difference between “Jeg ville drikke vand, hvis jeg var tørstig” and “Jeg ville have drukket vand, hvis jeg havde været tørstig”?

They’re both conditional, but refer to different time frames:

Jeg ville drikke vand, hvis jeg var tørstig.
→ Hypothetical present or general situation.
If I were (now / generally) thirsty, I would drink water.
Jeg ville have drukket vand, hvis jeg havde været tørstig.
→ Hypothetical past situation (that didn’t happen).
I would have drunk water, if I had been thirsty (but I wasn’t).

Formally:

ville + infinitive → would + base verb (present / general hypothetical)
ville have + past participle → would have + past participle (past hypothetical)

Do ville and English “would” always match in usage?

They overlap a lot, but not 100%.

Similar uses:

Conditional:
- Jeg ville drikke vand, hvis jeg var tørstig.
  I would drink water if I were thirsty.
Future in the past:
- Han sagde, at han ville komme.
  He said that he would come.

Differences / cautions:

English politeness “would you…?” often becomes vil du…? or kan du…? in Danish, not ville du…?:
- Would you help me? → Vil du hjælpe mig? / Kan du hjælpe mig?
English habitual “would” in the past often uses plejede at or simple past in Danish:
- When I was a child, I would play outside.
  → Da jeg var barn, plejede jeg at lege udenfor. or … legede jeg udenfor.

So ville often corresponds to “would”, but not in all idiomatic uses.

Can I drop the second jeg and say “Jeg ville drikke vand, hvis var tørstig”?

No. Danish is not a “pro-drop” language like Spanish or Italian; you must repeat the subject pronoun in the subordinate clause:

Correct: … hvis jeg var tørstig.
Incorrect: … hvis var tørstig.

Every finite clause (main or subordinate) normally needs an explicit subject.

How do you roughly pronounce “Jeg ville drikke vand, hvis jeg var tørstig”?

A simple, learner-friendly approximation:

Jeg – like “yai” (some say more like “yaih” or “yeh”)
ville – VIL-leh (short, clear v and l)
drikke – DREK-eh (with a soft “r”; close to “DREK-uh”)
vand – like van, very short; the final d isn’t pronounced as in English “d”
hvis – like vis (viss)
var – like English “var” in “varnish” but short
tørstig – TØR-stee, where ø is like the vowel in British “bird” or French “peur”

So very roughly:

Yai VIL-leh DREK-eh van, viss yai var TØR-stee.

Native Danish pronunciation will be more reduced and fluid, but this gets you close enough to be understood.