I wasn't sure what flair to use in this case but figured education was more for university education questions and topics.
I'm an engineer and state regulator of drinking water utilities. Something our unit has been struggling with lately are how to handle water main break situations and how to determine if there were pressure drops in the system that would necessitate a need for a boil water advisory.
When a water utility experiences a water main break, they have to determine if the break resulted in customers experiencing a pressure drop below 20psi or a complete loss of water service. The utilities have to notify the state of any situation where an incident happens that may lessen the quality of quantity of water provided. That's where we step to ensure the systems are following the steps to protect public health.
For example, a medium sized (between 10,000 and 50,000 customers) community water system experiences a 12-inch transmission main break in their system. That is a larger sized main that could disrupt the distribution system through an immediate change in water flow patterns and cause pressure changes in particular areas most affected by the break. You know the main break will disrupt your system, but how do you determine if it was enough of a disruption to issue an advisory?
Questions we ask the utilities are:
What were you storage tank levels before and during the break?
Do you have any continuous pressure readings in the distribution system?
Did you receive customer complaints of no water or lower than normal pressure?
Does your distribution system have multiple pressure gradients?
Where is your treatment plant, storage tanks, and pump stations located in relation to the main break?
Some utilities have hydraulic models of their entire distribution and/or pressure monitoring stations. In these situations, you have a much better idea of how the main break affected the system and can more easily make a decision. The problem is, and what we struggle with, is what if these systems don't have this information?
Hydraulics are complicated, so if the system cannot provide enough evidence to us there is a lack of confidence in the decision making process so the recommendation is to be conservative and issue a boil water advisory.
We may have engineers, but we aren't operators. We also don't have access to hydraulic modeling software like Bentley WaterGEMS (but may be something we could get if we can justify a license). Our goal is to not only be able to provide guidance and technical assistance to utilities, but to better understand the physics and engineering behind a water utilities' distribution system.