Кислотность воды выросла вплоть до того, что воду проверили на аммиак.

Because its subject is кислотность, and кислотность is a feminine noun.

In the past tense, Russian verbs agree with the subject in gender and number:

• masculine: вырос
• feminine: выросла
• neuter: выросло
• plural: выросли

So:

• Кислотность воды выросла = The acidity of the water increased

Because кислотность воды means the acidity of the water.

In Russian, one noun often modifies another by using the genitive case:

• цвет машины = the color of the car
• температура воздуха = the temperature of the air
• кислотность воды = the acidity of the water

So воды is genitive singular of вода.

It is an idiomatic expression meaning:

• to the point that
• so far that
• to such an extent that

So the structure is:

• X произошло вплоть до того, что Y
• X happened to such an extent that Y

In your sentence:

• Кислотность воды выросла вплоть до того, что воду проверили на аммиак.
• The acidity of the water increased to the point that the water was tested for ammonia.

This phrase emphasizes an extreme result or consequence.

Yes. A learner will often meet simpler alternatives such as:

• настолько..., что = so... that
• до такой степени, что = to such a degree that

For example:

• Кислотность воды настолько выросла, что воду проверили на аммиак.
• Кислотность воды выросла до такой степени, что воду проверили на аммиак.

These are very close in meaning. Вплоть до того, что can sound a bit stronger or more emphatic.

Because воду is the direct object of проверили.

The verb проверить / проверять takes a direct object in the accusative:

• проверить документ = to check a document
• проверить кровь = to test blood
• проверить воду = to test/check the water

Since вода is feminine singular, its accusative form is воду.

Because проверить на + accusative is a common pattern meaning:

• to test for
• to check for the presence of

Examples:

• проверить на вирусы = test for viruses
• проверить на сахар = test for sugar
• проверить на аммиак = test for ammonia

So воду проверили на аммиак literally means something like they checked the water for ammonia.

This is a very common Russian pattern: the 3rd person plural with no expressed subject can mean they in an indefinite sense, or in natural English:

• someone
• people
• it was done

So:

• воду проверили на аммиак

does not necessarily mean a specific they. It often just means:

• the water was tested for ammonia
• someone tested the water for ammonia

This is called an indefinite-personal construction.

Because the sentence presents both actions as completed events.

• выросла is perfective: the acidity rose / increased
• проверили is perfective: they tested / checked

Perfective aspect is natural here because the speaker is talking about a finished increase and the resulting completed action.

If you used imperfective forms, the meaning would change:

• росла = was increasing / used to increase
• проверяли = were testing / used to test

So the original sentence sounds like a report of what happened, not an ongoing process.

The word order is normal and natural, but Russian word order is flexible.

The sentence begins with the topic:

• Кислотность воды = the water’s acidity

Then comes the result:

• выросла вплоть до того, что...

Then the consequence:

• воду проверили на аммиак

You could rearrange parts for emphasis, but the original order is straightforward and easy to understand.

No. Вплоть has other uses too, usually with до:

• вплоть до пятницы = up to Friday
• вплоть до мелочей = down to the smallest details
• вплоть до того, что... = to the point that...

So in your sentence, it is part of a larger fixed expression. On its own, вплоть is not usually something beginners use freely; it is better to learn it in common combinations.

Yes. Кислотность means acidity, that is, the level or degree of acidity. It is the correct scientific or technical noun here.

Compare:

• кислотность воды = the acidity of the water
• кислота = acid

So the sentence is not saying acid in the water increased; it is saying the water became more acidic.