The Sewerage & Water Board draws Mississippi River water and treats it at the Carrollton and Algiers plants. That public treatment process is the city-scale story. The last mile—from distribution main to service line to a building's plumbing—is the address-scale story, and older housing, multi-unit buildings, restaurants, and hospitality properties can create very different testing and flow requirements.
Katrina belongs here as infrastructure history, not as a sales keyword. EPA's restoration report describes how power loss, low pressure, distribution breaks, flushing, disinfection, and bacteriological sampling affected the return to service. The practical lesson is simple: household carbon, softening, RO, and UV equipment do not overrule an SWBNO advisory.
For ordinary treatment decisions, start with the current SWBNO report and a clearly defined goal at the property. For an active pressure or boil event, use SWBNO's current-status information and wait for the official clearance.