sakki konbini de mizu wo kaimasita.

Japanese often leaves out the subject when it is clear from context.

So in さっき　コンビニ　で　水　を　買いました。, the speaker is usually understood to mean something like I bought water at the convenience store a little while ago, even though I is not said.

This is very normal in Japanese. If the subject is obvious, it is often omitted.

• 私はさっきコンビニで水を買いました。 = more explicit
• さっきコンビニで水を買いました。 = natural if the listener already knows who is being talked about

さっき means a little while ago, just now, or earlier.

It is a casual everyday word for recent past time.

Some related expressions:

• さっき = a little while ago, casual
• 今さっき = just now, very recent
• 先ほど（さきほど） = a little while ago, but more polite/formal

So さっき fits well in ordinary conversation.

Many Japanese time expressions do not take に, especially relative time words.

さっき is one of those words. So:

• さっき買いました。 = correct
• さっきに買いました。 = unnatural/incorrect

This is similar to other relative time expressions:

• 昨日買いました。 = I bought it yesterday.
• 今日行きます。 = I’ll go today.
• 明日会います。 = I’ll meet them tomorrow.

By contrast, に is often used with more specific points in time:

• 三時に行きます。 = I’ll go at 3.
• 月曜日に会います。 = I’ll meet them on Monday.

The particle で marks the place where an action happens.

Since buying is an action that takes place at a location, で is used:

• コンビニで買いました。 = bought it at the convenience store

This is one of the most basic uses of で.

Compare:

• 学校で勉強します。 = study at school
• レストランで食べます。 = eat at a restaurant

A common learner confusion is mixing up で and に:

• で = where an action happens
• に = destination, existence, or specific target in some cases

So here, コンビニで is correct because the store is the place where the action of buying happened.

The particle を marks the direct object of the verb — the thing that is acted on.

Here, the verb is 買いました (bought), and the thing being bought is 水 (water), so:

• 水を買いました。 = bought water

More examples:

• 本を読みます。 = read a book
• コーヒーを飲みます。 = drink coffee
• パンを食べました。 = ate bread

So in this sentence:

• コンビニで = where
• 水を = what
• 買いました = what action happened

Even though it is written を, the particle is pronounced お in modern Japanese.

So:

• 水を買いました is pronounced roughly like
• みずお かいました

The same is true whenever を is used as a particle.

Its special spelling mainly helps show its grammatical role.

The dictionary form is 買う（かう）.

買いました is the polite past form of 買う.

Breakdown:

• 買う = to buy
• 買いました = bought / have bought

This uses the polite -ます pattern:

• 買います = buy / will buy
• 買いました = bought

So if you want the casual past form, it would be:

• 買った = bought

Because the action already happened.

• 買います = buy / will buy
• 買いました = bought

Since さっき means a little while ago, the sentence is talking about the past, so 買いました is the natural form.

So these match:

• さっき + 買いました = correct
• さっき + 買います = usually wrong, because the time word and verb tense do not match

コンビニ is a borrowed word, originally from the English-based Japanese word convenience store.

Japanese often writes foreign loanwords in katakana, so:

• コンビニ = convenience store

It is actually a shortened form of コンビニエンスストア.

Katakana is commonly used for:

• loanwords
• foreign names
• sound effects
• emphasis sometimes

So seeing コンビニ in katakana is completely normal.

Japanese word order is more flexible than English, as long as the particles make the roles clear.

So these are all possible:

• さっきコンビニで水を買いました。
• さっき水をコンビニで買いました。
• コンビニでさっき水を買いました。

However, some orders sound more natural than others depending on emphasis.

The original order is very natural because it goes:

1. time: さっき
2. place: コンビニで
3. object: 水を
4. verb: 買いました

A good beginner rule is: time + place + object + verb

Also, the verb usually comes at the end.

It is polite because it ends in 買いました.

Japanese has different speech levels. Compare:

• さっきコンビニで水を買いました。 = polite
• さっきコンビニで水を買った。 = casual

The polite version is common when speaking to:

• people you do not know well
• teachers
• coworkers in many situations
• customers
• older people, depending on context

The casual version is common with:

• friends
• family
• people you are close to

No. Japanese is normally written without spaces.

So the standard written sentence is:

さっきコンビニで水を買いました。

Spaces are often added in beginner materials to make the sentence structure easier to see.

That means:

• さっき = time
• コンビニで = place
• 水を = object
• 買いました = verb

But in real Japanese text, you usually will not see those spaces.

Yes. This is a very common pattern.

You can use:

[place] で [object] を [verb]

Examples:

• スーパーで野菜を買いました。 = I bought vegetables at the supermarket.
• 店でシャツを買いました。 = I bought a shirt at the store.
• 自動販売機でお茶を買いました。 = I bought tea from a vending machine.

So the sentence is a good model for many similar expressions.