What is a common cause of backflow in water systems?

The common cause of backflow in water systems is cross-connections between potable (drinking) and non-potable (non-drinking) systems. A cross-connection is a physical link between a public water supply and a source of contamination. When there is a change in pressure within the system, such as during a sudden drop in pressure due to a water main break or high water demand, contaminated water from the non-potable source can flow back into the potable system, leading to potential health risks. This highlights the importance of proper system design and backflow prevention measures to ensure safe drinking water.

The other options mention factors that can impact water distribution but do not directly cause backflow. High water demand can lead to pressure fluctuations, but it is the cross-connections that specifically create a pathway for contaminants to enter clean water sources. Aging infrastructure may cause leaks or breaks but is not a direct cause of backflow. Natural disasters might disrupt water systems but, again, do not establish the conditions necessary for backflow without the presence of cross-connections.