Precinct owner Britomart Group blamed the incident on a new employee of the cleaning contractor not knowing the protocols for disposal of dirty water.
"We believe this to be an isolated incident," said group marketing director Sarah Hull.
Several waste disposal facilities were provided on site.
United Cleaning Services regional operations manager Salesh Mudaliar said the machine attendant was standing in for a colleague who was on sick leave.
The machine uses mechanical action and hot water pressure instead of chemicals.
Daniel Sansbury, who is acting manager of the council's natural resources and specialist input unit, said the machine collected its own waste.
This should be emptied in an appropriate container and disposed of at a waste facility, or through the wastewater system, with the agreement of Watercare Services.
Fines of up to $1000 could be issued for discharging contaminants to the stormwater system and people seeing discharges should call the Council Pollution Hotline.