Here's why Australians are being asked to water plants with milk

SBS Australia

14-07-2025

Utilities urge people not to tip fats, oils or grease down drains - Sydney Water is making clear that includes milk.
The fat in milk is a contributing factor to problematic fatbergs that block drains and cost millions to deal with.
There is an average of about 1300 'chokes' in Sydney's sewage system each month due to contaminants. The short shelf life of milk means many Australians have came across milk past its prime and chosen to dispose of it rather than drink it. But those who have tipped it down the kitchen sink drain are doing it wrong, according to Sydney Water.
Australian residents — not just those in Sydney — are being urged not to pour milk down the drain because of the potential damage it can cause.
Milk is part of the 'FOG' problem in drains
The key concern are the fats contained in milk.
Sydney Water's principal manager environment, Ben Armstrong spoke to SBS News about a new campaign that will focus on fats, oils and grease contaminants that should not go into drains. Source: Supplied "It's all foods or liquids that have fats in that we are keen for people not to put down the drain," Sydney Water's principal manager environment, Ben Armstrong, told SBS News.
"It adds to the buildup of fat and what we call 'fatbergs' in the system, and can create a lot of problems."
Fatbergs are large accumulations of items that are not designed to be flushed down toilets. Combined with fats, oils and greases — or 'FOGS' — they clump together and can cause blockages in drains. They can weigh in the tonnes and are difficult to pull apart and dislodge. Armstrong said recent Sydney Water survey results showed that 69 per cent of Sydneysiders thought it was okay to tip old milk down the drain. "That's quite a high percentage, so we're quite keen to raise awareness that the only things we want you to put down the sink is really water, soap and detergent," he said.
"It's been something that I guess people don't really realise and they've been doing it for quite a while."
While disposing of a small amount of milk down the drain might seem harmless, fats in milk contribute to blockages that have cost millions of dollars to deal with in Sydney in the past nine months alone. Source: Getty / Caner CIFTCI Sydney Water suggests people add water to old milk and pour it on plants.
Armstrong said only the three 'P's — pee, poo and paper — should be flushed down toilets, and only water, soap or detergent should go down sinks.
The fatberg that stopped a concert Armstrong said Sydney Water spent $12 million in the nine months to July dealing with 11,805 "chokes" in the wastewater system. He said the total cost of such blockages would likely be about double that if related costs in terms of the clean-up and repairs of cracked and broken wastewater infrastructure were also taken into account. In February, a blockage caused by a fatberg forced the last-minute cancellation of the concert of Canadian rock singer Bryan Adams, who had been set to play at Perth Arena.
Following the cancellation, the Water Corporation said the concert had not gone ahead "due to the risk of sewage backing up within the venue toilets, posing a potential public health risk".
The cumulative effect
Pouring a bit of milk down a kitchen drain might seem harmless, but the interconnected nature of drainage systems means it's not.
Professor Stuart Khan, head of the School of Civil Engineering at the University of Sydney, said the two main water drainage systems in cities are storm water and sewage drains, with sewage drains dealing with the wastewater from all parts of the household, including kitchens and bathrooms. "The sewage takes all of the indoors water, so everything that we flush down toilets that comes from the kitchen sink, the bathtub, the showers, they all connect within the household, within the property and then that water then is directed into a municipal sewer, which is the larger pipes that run ... often under the backyards or under the street out the front, and take the water to a sewage treatment plant," Khan told SBS News. "It's a cumulative effect, so it's not so much what a single person does, it's the impact of everybody in a city. Sydney has 5.5 million people — if we're all discharging fats, including the fats in milk down drains, then yes, that can lead to part of the problem further downstream where they all come together and you have the sewage of hundreds of thousands of people accumulating."
Many Australians would have poured spoiled milk down the sink without a second thought in the past, but the fats in milk are combining with other pollutants in our waste water to form blockages. Source: Getty / Robin Gentry Khan said the issue was not specific to Australia . "All of the big cities around the world are dealing with this problem," he said. "It does have a huge impact on maintenance needs, therefore it has a big impact on the water utility costs, and they all flow back to customer bills.
"So it's in all of our interests to try to minimise the need for maintenance, to try to minimise sewage spills and overflows which blockages can cause."
Greater public awareness While utilities may not have specifically articulated milk in the past as one of the things not to be put down drains, Khan said it was a good way to get the message across to the general public. "One of the advantages of talking specifically about milk, is that it has the reaction that I think it's caused here, which is to go, 'oh, right, so that contains fats, what else might contain fats?', so thinking about some of the less obvious sources of fat going down the drain," he said. "I think it is a way of sort of broadening our perspectives on what is okay and what's not okay to flush down the toilet or down the kitchen sink."
Sydney Water will launch its campaign focused on increasing awareness of the potential issues that fats, oils and greases can cause sewer systems on the weekend.