One of water's major but less celebrated uses is to help flush bathroom and other unwanted waste from homes and industry.
The sewerage system is made up of the small and large pipes, pumping stations and treatment plants which remove the city's waste. The largest sewers (trunk sewers) can be in excess of 4 metres in diameter, big enough to drive a car through, and a big engineering feat to construct.
Discharge from the Home
It's estimated that on average, we each discharge 220 to 275 litres of waste water to the sewerage system every day.
Household waste water is normally expected to be around 50% carbohydrate, 40% protein and 10% fat. The pH can range from 6.5 to 8.
But some waste water contains things which are very difficult to treat. Oil, grease, chemicals, nutrients, cotton tips, tampons, condoms and other plastic products don't take well to the natural processes used to break down waste and can end up out in the Bay.
In Melbourne we flush or empty about 370,000 million litres (megalitres) of waste water down into the sewerage system every year.
In order to reduce the non biological waste entering the treatment system, please place these items in a rubbish bin and not a drain or toilet.
Discharge in Industry
Years ago, dirty water, oil, grease and chemicals from industry and small businesses would just have gone untreated into rivers or the sewerage system for disposal.
In 1948 a by-law was introduced allowing certain trade waste into the sewerage system for treatment. City West Water and the other retail water companies in Melbourne continue to accept this waste for responsible treatment on a user pays basis.
More and more industries and organisations in Melbourne now sign strict agreements listing exactly what greasy waste, chemical or organic materials are in the liquid they need to dispose of down the sewerage system, how they will first treat the liquid to extract unacceptable substances and what volume they will be putting in the sewer and when.
What kind of industries do we have?
In our region we have industries making a wide variety of products and materials. These range from making cars, bottling/canning drinks, washing wool and dyeing denim and textiles. There are more than 3,000 industries and organisations registered with City West Water for trade waste services.
Apart from big factories, there are also small businesses - laundromats with soapy water, service stations with grease and oil, even restaurants and fast food outlets - which produce surprising amounts of what is called greasy waste from cooking in oils and washing up thousands of plates. These need special treatment.
What waste is allowed in industrial discharge?
YES - Approved waste from industry and businesses. The treatment plant needs to know what substances and, more importantly, what quantities it will be treating to ensure untreatable waste does not come through the plant. The Environment Protection Authority (EPA) provides City West Water with a license with strict guidelines that we must meet. Failure to do so means City West Water can be faced with fines for any damages.
NO - Here are some of the major substances that should not be in the sewer:
Waste containing any of 16 types of hazardous waste listed by the Environment Protection Authority as Priority Wastes:
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Floating layers of oil, fat or grease
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Free layers of organic liquids
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Fibrous material that could block the sewers
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Unstable latex emulsions containing paint, adhesive, rubber or plastic.