We find ourselves with a geographic description of where the temple is to be situated. Before we have that description we read about a river that shall flow from the temple and which will make all brackish water into fresh, except for one specific area. Water was, and still is, absolutely the most important resource in the Middle East. Wars have been, and continue to be, fought over who has access to water. The Golan Heights in Israel ostensible were captured for more territory, but in reality they provide access to water. Water in the middle east is like what oil was for some countries in WWII. It was a resource that necessitated going to war if ones access was denied.
This remains the case so when you have an image of water flowing from the temple then you know that it is meant to provide all that a people might need in order to prosper and thrive as a nation.