Final answer:
The water and detergent solution in the first sink needs to be changed when it becomes dirty or loses its effectiveness in cleaning the dishes.
Step-by-step explanation:
The water and detergent solution in the first sink needs to be changed when the water becomes dirty or when it loses its effectiveness in cleaning the dishes. The purpose of the first sink is to remove food particles and grease from the dishes. As the dishes are washed, the water in the sink can become dirty due to the food particles and grease that are being removed. Once the water becomes dirty, it is important to change it to maintain hygienic conditions and ensure effective cleaning.