For Actions, Questions & Projects around Circular Materials and Water. Consider also to add Tags to show Relations to other Categories.
Should we change this category to Water & Materials? Or decide where does water belong to?
I think if the question is about “water” in general “Materials” is a good category. If you have specific solutions other categories might be better (see “water” tag).
I would leave it with “Materials”. There are so many things that ask for other categories or belong in more than one category … this will always happen. Creating more categories or more complex categories is most likely not the best answer to this.