Which of the following is a type of bulk water storage system?

A water tank rack, commonly known as a "hippo," serves as a type of bulk water storage system because it is specifically designed to hold and store large quantities of water for various uses, such as emergency response, disaster relief, or military operations. These systems allow for the easy transport, accessibility, and distribution of water in large volumes, which is crucial during large-scale operations where water supply and management are critical.

In contrast, a water purifier is focused on treating and removing contaminants from water rather than storing it. A filtration unit serves a similar purpose as it is designed for the process of filtering water but does not itself store water after filtration. A desalination plant processes saltwater into fresh water but is not a storage system; it converts water rather than holding it in bulk. Therefore, among the given options, the water tank rack is the most appropriate choice for a bulk water storage system.