Final answer:
Backflow introduces contaminants into potable water due to pressure changes, which can be prevented by reverse osmosis—a water purification method that applies external pressure to reverse solvent flow through a membrane.
Step-by-step explanation:
The reverse flow of contaminants through a cross-connection into a potable water supply is known as backflow. Backflow can happen due to changes in pressure within the water system, and it poses a significant risk by allowing contaminants or pathogens to enter the clean water supply. One method to prevent such an occurrence is through reverse osmosis, which applies an external pressure greater than the osmotic pressure to force the flow of solvent (in this case, water) through a semipermeable membrane from a more concentrated to a less concentrated solution. This technique is crucial in water purification systems, including the treatment of seawater to produce drinkable water. It is an effective barrier against contamination and ensures the delivery of clean and safe water.