Could be analyzing waste water and come up with ads such as "I see you're running out of milk/juice/cocaine/whatever; would you like me to order some for you?"

Could be analyzing waste water and come up with ads such as "I see you're running out of milk/juice/cocaine/whatever; would you like me to order some for you?" or "Hey, your current brand of <whatever> is unhealthy/expensive/difficult-to-wash-off; I suggest <brand> instead; btw click here to order your free subscription". I would've hoped the current shortage of chips can put an end to this and 5G perma-surveillance, but here we are ... Edit: not to speak of "We've detected remnants of the XYZ strain of the <whatever> virus; please isolate yourself now. This message has been passed on to the ministry of health and education. Thanks for your cooperation."