What is the name of an above-ground water storage tank designed to maintain pressure in a water distribution system?

Answer: B — Elevated water storage tower

An elevated water storage tower is specifically designed to maintain pressure in a water distribution system by utilizing the force of gravity. By being positioned high above the ground, these towers allow for water to flow down into the distribution system, ensuring that adequate pressure is maintained throughout the network. This is crucial for supplying water effectively to various parts of a community or service area, particularly during peak demand periods or emergencies. In contrast, an underground reservoir is typically used for storage purposes but does not provide the same gravitational pressure benefits. A pressure tank, while it can help to maintain water pressure in certain systems, is different in that it primarily serves pump systems, providing water at a consistent pressure rather than directly contributing to a greater distribution system's pressure. Lastly, a supply reservoir refers more generally to a larger body of water held for various uses and does not indicate the elevated structure needed for pressure regulation. Thus, the elevated water storage tower is the appropriate answer due to its specific function in water pressure maintenance.