How are you supposed to clean up fire retardant dropped from a plane over a large area?
Edit: yes it moves it around, and just like the cleaning person at the office does you move it into the water table or drainage system. Or do you separate your dirt when you mop a floor or wash your clothes?
Removing dirt from the carpet and washing it down the drain is fine because ordinary "dirt" (i.e. soil) is made of non-toxic or biodegradable stuff. By contrast, washing toxic materials or heavy metals into the water table is the place you don't want them. There's a reason it's illegal to pour used motor oil down the drain.