Sewer blockages flush out worst offending suburbs

South Australians are heeding the ‘Healthy Sewers’ message and helping reduce blockages across SA Water’s wastewater network by being mindful of what they’re flushing or pouring down the drain, but some suburbs unfortunately remain top of the blockage leaderboard.

New figures show the total number of sewer blockages fell by 7.6 per cent in the past financial year, from 28,824 to 26,629.

There was an even stronger 20.4 per cent reduction recorded in the first 6 months of the 2026 calendar year compared to the same period in 2025.

Despite the improvement, Morphett Vale again recorded the state’s highest number of blockages during 2025-26 with 675 incidents, ahead of Rostrevor (403), Flagstaff Hill (372), Athelstone (343) and Happy Valley (335).

SA Water’s Senior Manager of Infrastructure, Planning and Strategy Dr Daniel Hoefel said the overall reduction was driven by fewer blockages caused by tree roots and wet wipes not certified as flushable.

“However, blockages caused by cooking fats, oils and grease – all things that should not be poured down the drain – increased from 914 to 971, making it one of the few preventable causes to rise,” Daniel said.

“Tree roots remained the leading cause, accounting for 17,392 incidents across our sewer network during the past financial year, down from 18,819 the previous year. This is particularly a challenge in established areas with mature trees, with the roots forcing their way into underground pipes in search of water.

“Blockages caused by wet wipes also fell from 1,203 to 1,045, while foreign objects – such as paper towel, tissues and even items such as kids’ toys – dropped from 687 to 598.”

Daniel said unlike tree roots, many blockages are preventable through simple changes at home.

“Our ongoing Healthy Sewers campaign continues to remind households that what goes down sinks and toilets can have a major impact underground and even cause issues on your own property,” he said.

“Fats, oils and grease can harden inside pipes, trapping other debris and restricting wastewater flows while non-certified wet wipes in particular can also create blockages when flushed, as unlike toilet paper, they’re not designed to break down in water.

“Sometimes, blockages in the pipes can also cause the sewage to come back up the way it came, overflowing into yards and bathrooms, resulting in an otherwise avoidable call to a plumber.”

Only the 4 Ps of pee, poo, (toilet) paper and things with proof of flushability should be flushed. Cooking fats and oils should be cooled and put in the bin, along with wipes and other household waste.

Main causes of sewer blockages (2025–26 compared to 2024-25)

1. Tree roots: 17,392 (down from 18,819)
2. Wet wipes: 1,045 (down from 1,203)
3. Fat build-up: 971 (up from 914)
4. Foreign objects (anything else that isn’t flushable): 598 (down from 687)

Highest number of sewer blockages by suburb (2025–26)

1. Morphett Vale: 675
2. Rostrevor: 403
3. Flagstaff Hill: 372
4. Athelstone: 343
5. Happy Valley: 335