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Protecting public health and the environment

Perth's wastewater system, like all wastewater systems around the world, is designed to protect our health and the environment.

Around 335 million litres of wastewater - the equivalent of 210 Olympic-sized swimming pools - is collected every day from households, commercial businesses and industries and directed to treatment plants, where the wastewater is treated to an environmentally acceptable standard before being reused, or safely discharged back to the environment.

Overflows can sometimes occur due to system failure caused by tree root intrusion, blockage by fats (from commercial grease traps), power interruption, asset failure or damage by third parties.

As the system is designed to protect public health, in an emergency situation wastewater will overflow to the environment so that it does not back up in pipes and flow into streets or people's homes.

	Perth's Wastewater System - Protecting our Health and our Environment

Wastewater overflows

Wastewater overflows have no long-term impact on the environment. Research shows that even a large overflow contributes a tiny fraction to the nitrogen and phosphorus levels already present in waterways from their broader catchments. Elevated levels of these nutrients can cause algal blooms.

Wastewater overflows can slightly reduce the levels of dissolved oxygen in the receiving water and can also contribute very small amounts of toxicants, such as heavy metals to the river system.  The quantities of the contaminants are too small to harm the organisms that live there.

The main impacts of a wastewater overflow are: the possible risk to human health through primary contact (if swimming) in water impacted by an overflow within the first 48 hours; and the inconvenience to river users.

As a precaution, a waterway may be temporarily closed while the Health Department determines if it is safe for primary contact.

The Water Corporation manage wastewater overflows using abatement programs, effective operations and maintenance of the wastewater system and by putting in place structural measures such as emergency storage tanks and by-passes.

Acknowledging that the Swan River is an icon and the economic, social and environmental importance of our waterways, we have carried out system upgrades costing millions of dollars to reduce the risk of overflows from occurring. But no matter how much is spent, this will never guarantee that overflows won’t occur.

The $15 million Riverwise Program completed in 2000 resulted in a decrease from an average of six to less than one overflow a year from riverside pump stations.

Over the last five years through the Wastewater Overflow Risk Management Program, we have invested  more than $100 million upgrading assets near our waterways to improve our abatement of overflows.  Works included enhancing emergency management provisions at wastewater pumping stations, pumps and pressure mains; replacing or relining wastewater sewers and preventing root blockages in wastewater reticulation sewers.