"The dog drinks its water."
Translation:Le chien boit son eau.
What you say makes sense. It's just another thing to remember in French.
My problem is not that I got it wrong or that I wasn't given any indication that this irregularity existed. My problem is the reason I was given for getting it wrong which I have copied from Duo and pasted below.
Le chien boit son eau.
eau is masculine, not feminine.
Getting the last question wrong on the last exercise required to receive a mastered rating will make a stronger impression on my memory than the couple of times I properly identified eau as feminine.
Perhaps someone should draw attention to Duo that they are teaching a fundamental error, misstating the gender of one of the more common words in French, and that they should take steps to correct it.
I reported it but the only option that applied was the given answer has a mistake or is misleading. As you pointed out the given answer is correct but not the reasons that they give for requiring that answer. The reasons are both incorrect and misleading.
But the reason given by Duo is that there are gender considerations and the answer given was incorrect because the wrong gender was applied. Duo clearly states the eau is masculine not feminine. That is incorrect.
In fact, there are no gender driven reasons for using son in this sentence. Son is used because over time the French have adapted their language to facilitate easy speech by removing gender considerations on some of those occasions when vowels collide.
Stating definitively that eau is masculine is incorrect and misleading for students. That should be rectified by Duo. The appropriate reason for judging the answer incorrect should be given.