kongetu no suidoudai ha omotta yori takakatta desu.

It means this month’s water bill.

• 今月 = this month
• 水道代 = water bill / water charges
• の connects them, showing that the water bill belongs to or relates to this month

So 今月の水道代 literally means the water bill of this month.

の is used to connect nouns.

Here, 今月 and 水道代 are both nouns, so の works like ’s or of in English:

• 今月の水道代 = this month’s water bill

This is one of the most common uses of の in Japanese.

は marks the topic of the sentence.

So in:

• 今月の水道代は…

the speaker is saying, as for this month’s water bill...

Everything after that gives information about that topic. In this sentence, the comment is that it was higher than expected.

Because the speaker is comparing reality with what they thought before.

• 思う = to think
• 思った = thought

So 思ったより means than I thought or than I had expected.

Using the past form makes sense because the thinking happened before the speaker found out the actual water bill.

Here, より means than in a comparison.

So:

• 思ったより高かった = was higher than I thought

A very common pattern is:

• A は 思ったより B
• A is more B than I thought

For example:

• 思ったより難しい = harder than I thought
• 思ったより寒かった = colder than I thought

Yes, something is omitted, but that is very normal in Japanese.

In English, we might say:

• It was higher than I thought it would be

In Japanese, the it would be part is often left out because it is understood from context. So 思ったより is a very natural shorthand for than I thought.

The full idea is something like:

• 今月の水道代は、（自分が）思ったより高かったです。
• This month’s water bill was higher than I thought (it would be).

Because 高い is an い-adjective, and い-adjectives make their own past form.

• 高い = high / expensive
• 高かった = was high / was expensive

Then です is added for politeness:

• 高かったです = was high / was expensive (polite)

So 高いでした is incorrect.

This is a very important pattern:

• 高い → 高かったです
• 安い → 安かったです
• 寒い → 寒かったです

In Japanese, です can be added after an い-adjective to make the sentence polite.

So:

• 高かった。 = It was high. / It was expensive.
• 高かったです。 = It was high. / It was expensive. (polite)

This is normal and very common in everyday polite speech.

Here it means expensive.

For prices, bills, fees, and costs, 高い often means:

• costly
• expensive
• higher than expected

So 今月の水道代は思ったより高かったです means the water bill was more expensive than expected, not physically high.

Yes, in this context it means water bill or water charges.

More literally:

• 水道 = water supply / running water
• 代 = charge / cost / fee

So 水道代 is the money you pay for water service.

A learner may also see 水道料金, which is also used for water charges. 水道代 is a common everyday way to say it.

Because Japanese often omits things that are clear from context.

In this sentence, 思ったより is a set expression meaning than I thought. The thing that was thought about is understood to be the amount of the water bill.

Japanese often leaves out subjects and objects when they are obvious, so this is completely natural.

Yes. That is also natural.

• 思ったより = than I thought
• 思っていたより = than I had been thinking / than I had expected

思っていたより can sound a little more like there was an expectation already in mind for some time. But in many everyday situations, both are fine and very similar.

Both are possible.

• 思ったより高かったです
• 思ったよりも高かったです

Both mean the same thing: It was higher than I thought.

よりも can add a little emphasis, but the basic meaning does not change much.

No. Normal Japanese writing does not usually use spaces between words.

The standard way to write this sentence is:

• 今月の水道代は思ったより高かったです。

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

The structure is:

• 今月の水道代 = this month’s water bill
• は = topic marker
• 思ったより = than I thought
• 高かったです = was high / was expensive

So the whole sentence means:

• As for this month’s water bill, it was higher than I thought.

Or more naturally in English:

• This month’s water bill was higher than I expected.