What is best way to address roommates cleanliness around bathroom, kitchen, microwave, vanity areas?

I am the homeowner and rent out 4 rooms. Although I provide a professional housekeeper out of my cost once a month to do spotless cleaning in general areas such as kitchen, living room, bathroom, and hallway areas, the roomies are under par with cleaning up after they cook, use the restroom, wash their hands around vanity area, and splatter bathroom with ?? liquids. I provide a microwave splatter shield and it does not get used every time, but no one cleans the splatter. We are all in our 30’s so all this "cleaning up after yourselves", should be pretty common sensed and simply courteous to all. How do I address without nagging? Do I post specific do’s and don’ts, have a meeting, leave notes, or address every time they happen? I am not an anal spotless freak, but all I ask is wiping down counters after cooking, wiping water after using vanity, wiping splatter on mirror, and especially inspecting and wiping toilet areas after using it. What is best way to address these ongoing issues? It does really bother me and I am trying so hard to keep my cool.
Another reason this bothers me is because the cleaning person charges me based on how much scrubbing, wiping, dusting, and time it takes to clean all areas mentioned. My cost gets affected when roomies don’t do their part to clean the mess they created.

Leave a Reply