What can generally be said about water after its usage?

Water's quality after usage typically diminishes due to the introduction of contaminants from various sources. This can include things like chemicals, biological matter, and other pollutants that enter the water system through agricultural runoff, industrial processes, or domestic wastewater. As a result, after water has been used, it generally becomes of lower quality compared to its original state.

While some applications may allow water to return to a level where it's still usable without extensive treatment, in most cases, the quality degradation means that it cannot be directly reused without some form of processing or purification. This diminishment in quality is why treatment plants exist—they work to restore water to a safe and usable condition, but it is not in its original pure form anymore.