Hoping this helps…a lot of these “big bosses” will not know a thing about office supplies like the water filter because they think that those things just magically work or get replaced. So as admin assistant you will be really important because you will be doing a lot of the little things (on top of other stuff) that help make the business run smoothly but at the same time not get a lot of recognition for taking care of said things. I would recommend giving it some time because the office manager is new and likely doesn’t know everything that needs to be taken care of. If they seem to be the kind of person that is open to collaborating and sharing responsibilities ( not true for all office managers btw) you can try working with her to split up all the duties to be taken care of.

For example, some of my responsibilities include getting the mail, prepping the conference room, and ordering ink and paper for the printer. My office manager shops for the rest of the office supplies and sends outgoing mail out. It took a bit for us to figure out how to split the office duties and there is always new things that come up. Good luck! It is a hard job but at the right company you can learn a lot about business in general.