Contaminated surface water

Requirements to discharge surface water

Directing stormwater, rainwater or groundwater to our wastewater system can overload it. If this happens, it can overflow. That's why all customers must manage excess water on-site by using bunding, stormwater drainage channels and roofing. You'll need to follow strict rules.

Discharge from open area 

We understand it's not practical to roof an area in some circumstances and the contaminated run-off can't be directed to the site stormwater system. In these situations, we may only permit the first 10 mm of rainfall collected in a first flush system to be discharged to the wastewater system. A first flush system collects and treats the first 10 mm of rainfall in an area designated contaminated by the NSW Environment Protection Authority (EPA) or local council. You must have our written approval to discharge this first flush volume to the wastewater system.

In all cases, the wastewater first flush volume must be treated to meet our acceptance standards before discharge.

We'll consider an application to discharge rainwater from contaminated open areas. However, you may need to provide:

  • evidence why the area can't be roofed to direct the rainwater to the site stormwater drainage system
  • a report from the EPA or local council confirming the run-off is contaminated and can't be directed to the site's stormwater drainage.

Discharge requirements

Our requirements differ depending on the size of the open area.

Open area < 50m2 Open area > 50m2

Install an approved first flush system designed to capture the first 500 litres of rainfall and direct the rest to the stormwater drainage system.

Install an approved first flush system designed to capture the first 10 mm of rainfall and direct the rest to the stormwater drainage system.

First flush volume to be pumped to sewer at a rate not exceeding 0.3 litres/second.

Install an approved rainfall cut-off device and delay discharge of first flush volume to wastewater system for at least one hour after rain stops.


Install a complete approved first flush system* in accordance with the manufacturer's specifications, designed to capture the first 10 mm of rainfall, or more if specified, and direct the rest to the stormwater drainage system.

*Fox Environmental Systems FF60

Excavation and construction

We won't permit you to discharge contaminated groundwater or surface water collected during excavation and construction to our system. You must treat and discharge it to the site stormwater drainage system. Talk to the NSW Environment Protection Authority (EPA) or your local council about their requirements.