Improper disposal of household chemicals—from bleaches and detergents to paints and pesticides—poses a significant threat to waterways and ecosystems. According to experts, the simple rule of thumb is: only the “three Ps”—pee, poo, and paper—should be flushed down the toilet, and only soap suds and water down the sink or shower.
Chemicals in the Home and Their Journey to the Environment
Modern households are stocked with a myriad of chemical products, many of which become environmental pollutants if not disposed of correctly. Prof Stuart Khan, an expert in water quality and treatment at the University of Sydney, notes that “thousands of different chemicals” flow down drains and into the sewerage system. These include herbicides and pesticides from food production, detergents and chlorine bleaches used in cleaning, and antibacterial agents and fragrances in personal care products.
When used or disposed of outside, substances like paints, oils, and petroleum-based solvents can enter the storm water system. “That’s a problem because storm water can run off into freshwater environments, local creeks and rivers, where if there are high concentrations of some of those chemicals you can have ecological consequences,” Khan warns.
The Three Ps: What Can Go Down the Drain
Jess Walker, head of the Western Treatment Plant and sewage transfer at Melbourne Water, emphasizes that every drain in the house—kitchen sink, shower, washing machine, and toilet—feeds into the same sewerage system. Pouring chemicals like fats, oils, paint, or harsh cleaners down drains can block pipes and disrupt the biological processes used in wastewater treatment.
Ben Armstrong, principal manager environment at Sydney Water, reinforces the rule: only the “three Ps”—pee, poo, and toilet paper—should be flushed. For sinks and showers, only soap suds and water should go down.
Hidden Chemicals and Their Long-Term Impact
Even trace amounts of chemicals can accumulate. A recent study of indoor dust and soil samples from across Victoria detected trace metals, Pfas (per- and polyfluoroalkyl substances)—commonly known as “forever chemicals”—pesticides, and pharmaceuticals, though most were below toxic thresholds.
Pharmaceuticals and antimicrobial agents like triclosan are not well removed by treatment systems, says Khan. “We get measurable concentrations of things like paracetamol and aspirin and ibuprofen and many, many other pharmaceutical type chemicals.” These can end up in the environment, affecting aquatic life.
Products containing Pfas—such as stain-resistant carpets, water-resistant clothing, and food packaging—can release these chemicals when washed, and they persist for hundreds of years. “The main problem with Pfas is its environmental longevity,” Khan explains. “It’s very, very slow to naturally degrade—potentially hundreds of years for some of these chemicals to degrade in the environment.”
Safe Disposal Methods and Alternatives
To minimize harm, experts recommend choosing low-toxic, phosphate-free cleaning products. The Victorian government’s Detox Your Home program suggests using baking soda or fibre cloths for scrubbing, and a vinegar-water solution for surfaces. Washing in hot water can disinfect effectively without relying on chlorine bleach or ammonia.
For outdoor activities, Melbourne Water advises: “If it’s not rainwater, it doesn’t belong in a storm water drain.” This rule covers most situations, says Walker. Chemicals washed into gutters or drains find their way into rivers, creeks, and oceans, usually without treatment, leading to algal blooms and wildlife harm.
In the garden, use compost and mulch instead of synthetic fertilisers, and opt for vinegar, hot water, or manual weeding instead of herbicides. When washing your car, do it on the grass or use a commercial wash.
For proper disposal of paints, chemicals, herbicides, and pesticides, take them to approved collection points. Many local councils offer chemical collections or drop-off points, and unused medicines can be returned to pharmacies.
Consumer choices can have a significant impact, as seen with the shift towards phosphorus-free detergents, which reduced environmental discharge. By following these guidelines, households can protect both their pipes and the waterways at the end of them.
