What Household Chemicals Should Never Go Down the Drain
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- Prof Stuart Khan of the University of Sydney said thousands of different chemicals flow down household drains into the sewerage system, including herbicides, detergents, chlorine bleaches, antibacterial agents and fragrances.
- A recent Victorian study of indoor dust and soil samples detected trace metals, PFAS 'forever chemicals,' pesticides, fossil fuel combustion products and pharmaceuticals including antibiotics, antidepressants and anti-inflammatories.
- PFAS compounds from products like stain-resistant carpets, water-resistant clothing, food packaging and cosmetics can take hundreds of years to naturally degrade once they reach the environment, Khan said.
- Sydney's sewage flows mostly to three ocean outfalls — Malabar, Bondi and North Head — with quite limited treatment along the way, meaning many chemicals are barely removed before discharge.
- Sydney Water's Ben Armstrong said the only items safe to flush are the 'three Ps': pee, poo and (toilet) paper, while sinks and showers should see only soap suds and water.
- Melbourne Water's Jess Walker warned that anything other than rainwater — including paint, chemicals, herbicides, pesticides and pool water — should never enter storm water drains and must be taken to approved collection points.
- Pharmaceuticals including paracetamol, aspirin and ibuprofen pass through wastewater treatment systems at measurable concentrations because antimicrobial agents and drugs are not well removed, Khan said.
Why it matters: Sydney's three ocean outfalls (Malabar, Bondi, North Head) discharge sewage with limited treatment, so chemicals flushed from homes — including PFAS, pharmaceuticals and pesticides — enter marine environments largely intact. The earlier consumer shift to phosphorus-free detergents has already reduced environmental discharge, showing individual disposal decisions scale into measurable water-quality outcomes.
