Vodácká helma je ve vodotěsném vaku.

Vodácká comes from vodák, a person who does recreational boating, canoeing, rafting, kayaking, and similar water sports.

So vodácká helma means a boating/watersports helmet, often best understood as something like a kayaking helmet or rafting helmet, depending on context.

Grammatically, vodácká is an adjective and it agrees with helma.

Because helma is a feminine singular noun.

In Czech, adjectives must agree with the noun in:

• gender
• number
• case

Since helma is feminine singular in the nominative here, the adjective also has the feminine singular nominative ending:

• masculine: vodácký
• feminine: vodácká
• neuter: vodácké

So:

• vodácká helma = correct
• vodácký helma = incorrect

Because the two nouns have different grammatical roles in the sentence.

• helma is the subject, so it is in the nominative
• ve vodotěsném vaku is a prepositional phrase meaning location, so vak is in the locative

So:

• helma → nominative singular
• vak → locative singular: vaku

This is very common in Czech:

• the thing doing/being something stays in nominative
• the noun after v/ve for location goes into the locative

Ve is just a pronunciation-friendly variant of v.

Czech often uses ve instead of v when the next word would make pronunciation awkward. Both mean in.

Here:

• ve vodotěsném vaku

Using ve is smoother than v vodotěsném vaku, which would be clumsy to pronounce because of the repeated v sound.

So:

• v = normal short form
• ve = easier-to-pronounce form used before some words

Because after v/ve when you mean location (in something), Czech uses the locative case.

The dictionary forms are:

• vodotěsný = waterproof
• vak = bag / sack / dry bag

But after ve, they change to locative singular:

• vodotěsném
• vaku

So:

• dictionary form: vodotěsný vak
• after ve: ve vodotěsném vaku

Both the adjective and the noun must change because they must match in case, gender, and number.

It is locative singular.

Why?

• the preposition v/ve meaning in usually takes the locative when expressing location

Breakdown:

• ve = in
• vodotěsném = locative singular of vodotěsný
• vaku = locative singular of vak

So the whole phrase means in the waterproof bag.

Vak is masculine inanimate.

You can tell from the dictionary form ten vak and from its pattern of adjective agreement and case endings.

For example:

• nominative singular: vodotěsný vak
• locative singular: ve vodotěsném vaku

That -ém adjective ending and -u noun ending fit a masculine singular noun in the locative.

In this sentence, je is normally kept.

• je = is
• it is the 3rd person singular form of být (to be)

Czech often omits pronouns like he, she, it, but the verb itself usually stays:

• Helma je ve vaku. = The helmet is in the bag.

In casual notes or headlines, people may drop things, but in a normal full sentence, je should be there.

Yes, there can be.

• vak often suggests a sack, gear bag, or specialized bag
• taška is a more general bag

In outdoor or water-sports contexts, vodotěsný vak is a very natural phrase for a waterproof bag/dry bag.

So in this sentence, vak sounds more appropriate than taška.

Yes. Czech word order is more flexible than English.

The neutral order here is:

• Vodácká helma je ve vodotěsném vaku.

But you could also say:

• Ve vodotěsném vaku je vodácká helma.

That version puts more focus on the location, something like:

• In the waterproof bag, there is a watersports helmet.

Both are grammatical. The difference is mainly in emphasis and information structure, not basic meaning.

A rough English-friendly guide:

• vodácká ≈ vo-DAATS-kaa
• helma ≈ HEL-ma
• je ≈ ye
• ve ≈ veh
• vodotěsném ≈ vo-do-TYES-naym
• vaku ≈ VA-koo

A few helpful pronunciation notes:

• á is a long vowel
• ě often softens the preceding consonant, so tě sounds roughly like tye
• j is pronounced like English y
• stress in Czech is usually on the first syllable of the word

Because Czech has no articles.

So Vodácká helma je ve vodotěsném vaku can mean:

• The watersports helmet is in the waterproof bag
• A watersports helmet is in a waterproof bag

Which one sounds best depends on context. Czech leaves that unstated unless another word makes it clear.

Here are the dictionary forms:

• vodácká → vodácký
• helma → helma
• je → být
• ve → v
• vodotěsném → vodotěsný
• vaku → vak

This is useful because when you look words up, adjectives and nouns are usually listed in their base forms, not in the exact forms used in the sentence.