Drenaż jest dobry.

Jest is the 3rd person singular present form of być (to be), so here it means is.

• drenaż = the subject
• jest = is
• dobry = good

So the structure is very similar to English: [noun] + is + [adjective].

Because Polish adjectives must agree with the noun in gender, number, and case.

Drenaż is a masculine singular noun, so the adjective also has to be masculine singular:

• masculine: dobry
• feminine: dobra
• neuter: dobre

That is why the sentence is Drenaż jest dobry.

A very common clue in Polish is the ending.

Most singular nouns that end in a consonant are masculine, and drenaż ends in -ż, which is a consonant sound. So learners will normally treat drenaż as masculine.

Because after jest with an adjective, Polish normally uses the nominative form.

So:

• Drenaż jest dobry. = correct
• dobrym would not be the normal form here

This can confuse learners because predicate nouns are often different, for example:

• On jest lekarzem. = He is a doctor.

But with a predicate adjective, Polish uses the plain nominative form:

• On jest dobry.
• Kawa jest zimna.
• Drenaż jest dobry.

It is in the nominative singular, because it is the subject of the sentence.

The adjective dobry is also nominative singular masculine, because it agrees with drenaż.

Polish does not have articles.

So Drenaż jest dobry can mean:

• The drainage is good
• A drainage system is good
• just Drainage is good

The exact meaning depends on context.

Normally, no. In a standard sentence like this, you should keep jest.

So the normal form is:

• Drenaż jest dobry.

Leaving it out would sound nonstandard, poetic, or very elliptical in most situations. Unlike some other Slavic languages, Polish usually keeps the present-tense form of to be.

Yes, Polish word order is fairly flexible, but the neutral, basic order here is:

• Drenaż jest dobry.

If you change the order, you usually change the emphasis:

• Dobry jest drenaż. = more marked; it emphasizes good
• Drenaż dobry jest. = unusual, poetic, or stylized

So for a learner, Drenaż jest dobry is the safest and most natural version.

Because dobry is an adjective, and it describes the noun drenaż.

• dobry = good
• dobrze = well

So:

• Drenaż jest dobry. = The drainage is good.
• Drenaż działa dobrze. = The drainage works well.

English often uses good and well in similar areas, so this is a common learner question.

A rough English-friendly approximation is:

DRE-nazh yest DO-bri

A few helpful points:

• ż sounds roughly like the s in measure
• jest sounds like yest
• r is usually tapped or rolled more than in English
• stress in Polish is usually on the second-to-last syllable, so:
  • DRE-naż
  • DO-bry

You add nie before jest:

• Drenaż nie jest dobry. = The drainage is not good.

That is the normal way to negate this kind of sentence.

Not always in a narrow sense. Dobry can mean things like:

• good in quality
• effective
• suitable
• beneficial

So in context, Drenaż jest dobry could mean not only the drainage is good, but also something closer to the drainage is effective or the drainage is satisfactory, depending on the situation.