DWF
Dry Weather Flow(1) Turns drilling fluid flow on. (2) Turns air on.; is the base flow in a sewer prior to rain induced flows.
DWI
Dry Weather InflowWater discharged into a sewer system and service connections from sources on the surface.; is the result of flow entering the collection system from connected sources which are not caused by rainfall. Typically, this could include water from fire fighting, hydrant abuse, street washing, sump pumps etc.