This video discusses the purpose and function of elevated water storage tanks. The job of finding enough water, making it safe to use, and then reliably distributing it to the system customers with almost no downtime is a monumental task that requires a lot of infrastructure. And, probably the most visible component of a public water system is the elevated storage tank, also known as a water tower.
Water hammer can work in both directions, and I only discussed one of those in the previous video (https://youtu.be/xoLmVFAFjn4). This episode revisits that demonstration to show how water hammer can form a vacuum pressure in a pipe. Momentum carrying fluid away from a valve wants to keep going even after the valve is closed. This generates a negative pressure than can cause major damage!