What is an example of a scenario that would lead to zero or negative pressure in a water system?

A water main break is a scenario that can lead to zero or negative pressure in a water system. When a water main experiences a break, it results in a sudden loss of pressure within the affected section of the distribution system. This can cause a significant influx of air into the system, potentially leading to conditions of zero pressure, especially if the break is substantial. The water flowing out of the break can create a vacuum effect and even reverse the flow of water, allowing contaminants from the surrounding soil or atmosphere to enter the system, posing a risk to water quality and supply.

In contrast, scenarios like increased water production, routine maintenance, or processes related to water purification typically do not create conditions that lead to zero or negative pressure. Increased water production would generally contribute to maintaining or increasing system pressure, while routine maintenance is often planned to prevent such issues. Water purification processes, although they might temporarily affect pressure in localized areas, are not likely to cause widespread negative pressure throughout the entire system.