Suljen hanan heti, ettei vettä valu turhaan, ja tarkistan putken uudestaan.

Finnish often leaves out personal pronouns when the verb ending already shows who is doing the action.

• suljen = I close
• tarkistan = I check / inspect

So minä is not necessary here. You could say Minä suljen..., but that would usually add emphasis.

Finnish does not have a separate future tense. The present tense is used for both present and future meaning, depending on context.

So:

• Suljen hanan heti can mean I close the tap right away or I'll close the tap right away
• tarkistan putken uudestaan can mean I check the pipe again or I'll check the pipe again

Words like heti and the situation make the future meaning clear.

They are objects, and in Finnish a singular total object in an affirmative clause often has a form that looks like the genitive:

• hana → hanan
• putki → putken

This usually suggests the action affects the object as a whole:

• suljen hanan = I close the tap completely
• tarkistan putken = I check the pipe as a whole

This is a very common Finnish pattern.

ettei is a combination of:

• että = that
• ei = not

Together, ettei introduces a negative subordinate clause. In this sentence it has a purpose/prevention sense:

• ettei vettä valu turhaan = so that water doesn't flow unnecessarily

So it is not just random negation; it links the reason or purpose for closing the tap.

Because Finnish negative clauses use a special form of the main verb.

The normal positive form is:

• vettä valuu = water flows / is flowing

But in a negative clause, the negative element carries the person, and the main verb appears in the connegative form:

• ei valu
• ettei ... valu

So:

• valuu = positive 3rd person singular
• valu = form used after negation

That is why ettei vettä valu is correct, not ettei vettä valuu.

Here vettä refers to an unspecified amount of water, not to the water as one complete, definite thing.

Finnish often uses the partitive with:

• mass nouns like water
• indefinite amounts
• clauses of flowing, leaking, existing, etc.
• especially negative clauses

So:

• vettä valuu = water is flowing
• ettei vettä valu = so that no water flows / so that water doesn't flow

Also, vettä here is not a direct object. It is the thing that would be flowing.

turhaan means:

• unnecessarily
• for nothing
• in vain
• needlessly

In this sentence, the most natural meaning is unnecessarily / needlessly:

• ettei vettä valu turhaan = so that water doesn't flow unnecessarily

uudestaan means again or once more.

So:

• tarkistan putken uudestaan = I check the pipe again

Yes, uudelleen is often possible too. The difference is usually small:

• uudestaan = very common and natural in everyday Finnish
• uudelleen = often a bit more formal or stylistically neutral in writing

In this sentence, uudestaan sounds perfectly natural.

Because that part is a subordinate clause, and Finnish normally separates subordinate clauses with commas.

The structure is:

• Suljen hanan heti = main clause
• ettei vettä valu turhaan = subordinate clause
• ja tarkistan putken uudestaan = another main clause

Since the subordinate clause is inserted between the two main parts, it gets commas on both sides.

Finnish has no articles, so it does not have separate words for a and the.

Instead, definiteness usually comes from:

• context
• word choice
• sentence structure
• what the speakers already know

So hanan and putken can naturally mean the tap and the pipe here because the situation makes them specific.

Finnish word order is fairly flexible, though some versions sound more neutral than others.

The sentence as given is natural and neutral:

• Suljen hanan heti...

But Finnish can move adverbs for emphasis, for example:

• Suljen heti hanan... = also possible
• Heti suljen hanan... = more marked or emphatic

So word order in Finnish is not as rigid as in English, but changing it often changes emphasis or style.