I used to work in the water industry and its fine for residue from biodegradeable detergents to be discharged into storm drains (in some countries it is illegal to wash your car in the driveway),if a water authority wanted to prosecute over this or close a business down it would have to be on the back of huge legislation concerning carwashing, jetwashing, street cleaning vehicles industrial window cleaners etc. The only thing we used to stop these businesses doing was using hosepipes during bans- on board water carriers can argue they collected water over winter in water butts etc and even if they test positive for chlorine they can say they added it themself.
P.s my tank has arrived.!!