Sewer and stormwater are two separate networks with different jobs. The sewer carries wastewater to treatment plants; stormwater carries rainwater to creeks, rivers and the bay largely untreated. They must never mix.
Why cross-connections are a serious problem:
- Stormwater into sewer: a single roof in a storm can send more water into the sewer than the household produces in days. Multiplied across properties, this overloads the network and causes sewage overflows — sometimes into homes and waterways.
- Sewer into stormwater: wastewater discharging to the stormwater system flows raw into local creeks. This is a pollution offence with significant penalties.
Cross-connections are usually inherited rather than deliberate — a downpipe plumbed into a convenient nearby pipe decades ago, a laundry outlet run to the stormwater, or a renovation shortcut. They often come to light during CCTV inspections, dye testing or when the utility investigates overflows in the area.
If an inspection finds a cross-connection on your property, it needs to be corrected by properly separating the systems. If you are unsure where your downpipes or fixtures actually discharge, a dye test is a quick way to trace them — coloured dye flushed into the fixture shows up wherever the pipe really goes.