Is a Hydrologic Unit the equivalent of the amount of TDS?
No.
The United States Geological Survey (USGS) monitors the quantity and quality of surface and ground waters throughout the nation. The USGS organizes watersheds or drainage basins of the United States into a hydrologic system that divides and subdivides the United States into successively smaller watersheds.
It looks like a scaling system based on watershed to account for areas of water geographically, but doesn’t represent water quality - more for dividing & sub-dividing areas of water containment, depletion & waste.
