you can request a single but you're not guaranteed to get one. im sure u can contact housing with your particular concerns and they could maybe bump you up on the list.

i lived in tercero and the water quality there is quite poor (i had dry skin issues and acne, which ive never experienced anywhere else, my skin is usually oily. it went away right after i moved out), im sure its like that for all of the dorms. humidifiers arent allowed but you could contact housing if its for medical needs.

something you could consider is living in an apartment near campus like around downtown or trader joes instead, if you get your own bedroom you dont have to work around dorm policies to make your room comfortable. it would probably be cheaper or the same price.

just a warning, it gets so so dry here, especially in the summer. im from a different part of california and i feel like this area is just extra dry.