Person A puts things in the sink, as dishwasher is on, at some point water from various sources (cooking, tumble drier, rinsing a bowl out) was put into sink and a mug was filled at some point with water from some source.
Person B needs to take paracetamol,and decides to drink the water in the mug in the sink.
Person B starts gagging and making wretching noises and asks Person A what is in the mug, and implies that Person A shouldn't have left that water in the mug.
Person A thinks that Person B shouldn't have drunk random sink water,and should have used the glasses and fresh tap water right next to the sink.
So, was Person A wrong to leave the random water in the mug. Or was Person B wrong to drink the random water and then blame person A for being "poisoned".