Learn Hardcore German: Ich werde das Wasser vorsichtig in den Topf hineingießen. - I will carefully pour the water into the pot.

Yes. German very often uses the present tense for near-future plans. The future with werden adds a sense of intention or a more “future-looking” tone. Both are fine here:

Future: Ich werde das Wasser vorsichtig in den Topf hineingießen.
Present for a planned action: Ich gieße das Wasser gleich vorsichtig in den Topf.

Why is the verb at the very end?

German main clauses are V2 (finite verb in 2nd position). With a helper like werden, the main verb appears as an infinitive at the end:

Finite verb in 2nd position: werde
Infinitive at the end: hineingießen So: Ich [1] werde [2] ... [hineingießen].

Is hineingießen a separable verb? How does it behave in other tenses?

Yes. hinein- is a separable particle.

Present: Ich gieße das Wasser in den Topf hinein.
Simple past: Ich goss das Wasser in den Topf hinein.
Perfect: Ich habe das Wasser in den Topf hineingegossen.
With a helper (like in your sentence), the infinitive is written together: hineingießen at the end.

Do I need hinein if I already say in den Topf?

Not strictly. in den Topf gießen already means “pour into the pot.” hinein reinforces the direction “into” and can sound a bit more explicit or “complete.”

Without the particle: Ich werde das Wasser vorsichtig in den Topf gießen.
With the particle (emphasis on movement into): Ich werde das Wasser vorsichtig in den Topf hineingießen.

Why is it in den Topf and not im Topf?

Because in is a two-way preposition:

Accusative (motion toward/into): in den Topf (into the pot)
Dative (location/state): im Topf (= in dem Topf, in the pot) Here, there’s movement into, so accusative: in den Topf.

Why den and not dem or das?

Topf is masculine (der Topf). In the accusative, masculine takes den:

Nominative: der Topf
Accusative: den Topf
Dative: dem Topf So: in den Topf for motion into.

Can I say ins Topf?

No. ins is the contraction of in das and only works with neuter nouns. Topf is masculine, so you must say in den Topf (no standard contraction). You could say ins Glas (because das Glas is neuter).

What case is das Wasser here, and why das?

das Wasser is the direct object, so accusative. Neuter nouns use das in both nominative and accusative, so it looks the same. That’s why you see das.

Where should vorsichtig go? Can it move?

vorsichtig is a manner adverb. A common order is Time–Manner–Place, so placing vorsichtig before the place phrase is natural:

Natural: Ich werde das Wasser vorsichtig in den Topf (hinein)gießen. It can move for emphasis, but keep it close to the verb or object:
Also possible (focus on “carefully”): Ich werde vorsichtig das Wasser in den Topf hineingießen. Avoid scattering it too far from the verb; your original placement is ideal.

What’s the difference between gießen, schütten, einschenken, and eingießen/hineingießen?

gießen: neutral “to pour” (also “to water” plants). Ich gieße Wasser in den Topf.
schütten: to dump/pour (often fast or carelessly, also for solids like rice). Er schüttet das Wasser in den Topf.
einschenken: to pour a drink for someone (into a cup/glass). Sie schenkt Wasser ein.
eingießen/hineingießen: to pour into something; hinein- highlights movement into the inside of a container. Your sentence’s hineingießen makes that very explicit.
Also common: aufgießen for adding hot water to tea/instant foods.

What’s the difference between hinein, herein, and rein?

hinein: movement inward, away from the speaker’s location point of view.
herein: movement inward toward the speaker.
rein: colloquial for hinein/herein; with verbs you’ll hear reingießen in speech. In practice, with containers you’ll usually say hinein or just omit the particle: in den Topf (rein/hinein)gießen. Standard writing prefers hinein.

Why is gießen spelled with ß? When do I use ß vs ss?

Use ß after a long vowel or diphthong; use ss after a short vowel.

Long vowel: gießen (long “ie” + ß), Fuß
Short vowel: lassen, Fluss So gießen takes ß.

Any quick pronunciation tips for tricky parts?

gießen: “ie” = long “ee”; ß = unvoiced “s” → “GEE-sen.”
Topf: pronounce the pf cluster; it’s like “toppf.”
vorsichtig: “ch” here is the soft “ich-sound” [ç] → “for-ZIÇ-tich.”
hineingießen: stress the particle → hi-NEIN-gie-ßen.

How do I negate this sentence?

Place nicht before what you’re negating:

Negate the location (not into the pot): Ich werde das Wasser nicht in den Topf hineingießen (sondern in die Pfanne).
Negate the object (not the water): Ich werde nicht das Wasser in den Topf hineingießen, sondern die Milch.
Negate the whole action (contextual): Ich werde das Wasser nicht hineingießen.

Can I front something else for emphasis, like Das Wasser or In den Topf?

Yes, German allows topicalization; the finite verb still stays in 2nd position:

Object first: Das Wasser werde ich vorsichtig in den Topf hineingießen.
Place first: In den Topf werde ich das Wasser vorsichtig hineingießen. This changes focus but not the basic meaning.

Should hinein be written together with gießen here, or as two words?

In the infinitive/participle form used with helpers, write it as one word: hineingießen, hineingegossen. You separate only in the finite, main-clause form: Ich gieße … hinein.