から vs ので

[Pep95]

I understand that with から the emphasis is placed on the cause, and with ので the emphasis is placed on the effect.

I got this as an exercise today, and am wondering why I am wrong here. Isn’t the cause of the shopping the lack of water?

In the case of a sentence like “Since it’s Saturday, I am going to the party”, the cause of you going to the party isn’t because today is Saturday. But in the sentence above, I think the water shortage is the cause of the shopping spree. Can anyone clear this up for me?

[Kokusaibu]

I think it should be ので because the cause is external forces beyond the speaker’s volition or control.

However I’ve been confused by many of these. So out of interest I ran the から and ので examples by a native speaker. In about a third of examples their answer differed from the website, so I’m glad it’s not just me.

For example why does this sentence use から …

明日は月曜日だから、仕事に行く。
Because tomorrow is Monday, I will go to work.

…when these examples use ので?

土曜日なので、旅行に行きたい。
Because it is Saturday, I want to go on a trip.

今日は一月二十日なので、彼の誕生日です。
Since today is January 20th, it is his birthday.