High velocities in undersized water piping may cause what issue?

High velocities in undersized water piping can lead to negative pressure conditions within the system. When water flows rapidly through a pipe that is not adequately sized to handle the volume, it can create a vacuum effect, particularly upon sudden changes in flow or direction. This vacuum effect can result in negative pressure, which can draw contaminants or air into the system, compromising water quality and system integrity.

Understanding the implications of negative pressure is crucial for maintaining safe and effective water distribution systems. It can also lead to cavitation, potentially causing damage to pipes and fittings, or induce backflow, where unapproved water sources may enter the potable supply. Thus, managing water velocities and ensuring proper pipe sizing are critical aspects of backflow prevention and overall plumbing system health.