Grammar: understanding ～での, particle usage for なった, function of ため


Link: <https://www.kanaloco.jp/news/government/article-905621.html>

> プール管理の担当教員が水泳の授業での新型コロナウイルス感染を防ぐために、プールの水を常にあふれさせて水質をきれいにする必要があると勘違いしたことが原因。

Why is there a の after 水泳の授業で?

> 同月２日の検針時に学校全体の水道料金が、コロナ禍で水泳の授業がなかった一昨年の１１倍となったため発覚した

Why don't we use をなった here? Also, what is the function of ため here ("for" seems
not to make sense?)?




> Why is there a の after 水泳の授業で?

This の is a plain possessive particle. 水泳の授業で directly modifies 新型コロナウイルス. で
is the location particle and is used to specify _where_ Coronavirus is
happening. Therefore「水泳の授業での新型コロナウイルス感染」means "Coronavirus infection _in_
swimming class." See this related question for more information: [using の with
と,で, から, まで](https://japanese.stackexchange.com/questions/33605)

> Why don't we use をなった here? Also, what is the function of ため here ("for"
> seems not to make sense?)?

をなった won't work here. となる is a variant of になる. See this question for
differences between two: [What is the difference between 〜となる and
〜になる?](https://japanese.stackexchange.com/questions/108/)

ため here is used to specify the reason why 水道料金 came to light (発覚した). ため has
two meanings: in order to (or "for" like you mentioned) or because/since.




> Why is there a の after 水泳の授業で?

This の is a plain possessive particle. 水泳の授業で directly modifies 新型コロナウイルス. で
is the location particle and is used to specify _where_ Coronavirus is
happening. Therefore「水泳の授業での新型コロナウイルス感染」means "Coronavirus infection _in_
swimming class." See this related question for more information: [using の with
と,で, から, まで](https://japanese.stackexchange.com/questions/33605)

> Why don't we use をなった here? Also, what is the function of ため here ("for"
> seems not to make sense?)?

をなった won't work here. となる is a variant of になる. See this question for
differences between two: [What is the difference between 〜となる and
〜になる?](https://japanese.stackexchange.com/questions/108/)

ため here is used to specify the reason why 水道料金 came to light (発覚した). ため has
two meanings: in order to (or "for" like you mentioned) or because/since.

