They are among Australia's oldest pipes, carrying number ones and twos under some of the Harbour City's most historic suburbs since 1857.

Key points: Areas that are affected by the works are among the country's most densely populated

Areas that are affected by the works are among the country's most densely populated Residents and business owners have described the disruption as "a nightmare"

Residents and business owners have described the disruption as "a nightmare" Sydney Water says replacing the convict-era sewers will reduce "nuisance odour"

The convict-era sewers beneath the densely populated areas of Woolloomooloo, Darlinghurst and Potts Point are the last in Sydney to be replaced.

But some residents and business owners are up in arms, saying the work — which began in 2017 and affects an estimated 30,000 properties — creates "horrific noise" and causes unacceptable disruption to their lives.

Darlinghurst woman Diane Green said the project had the potential to kill her Airbnb business.

"It's so horrific I've had to refund guests their money ... you can't even have a conversation without shouting," she said.

"If I cancel my listings I lose my status ... I have spent a year building up the house to be my main income earner.

"I have a mortgage to pay, I'm getting very stressed."

Workers lay Sydney's first sewers under Pitt Street in 1857. ( Supplied: National Library of Australia )

One of the main complaints is about noise, with rock-breaking and loud drilling keeping people awake.

Wastewater and stormwater travel in the same pipes through the area — meaning during heavy rain and flash flooding the streets often stink.

Sydney Water is separating them into separate streams, and says the "Refresh Woolloomooloo" project will reduce "nuisance odour" and protect public health.

It also says it will improve the environment by reducing wet weather wastewater overflows into Sydney Harbour.

'It needed to be done'

Jesse James, owner of a boutique hotel on Darlinghurst Road, said his business had been subjected to relentless noise at night and demanded compensation for local businesses.

"There would be huge discrepancies as to when they would be working so we would move guests to other rooms that were quieter and then work hours changed," he said.

Across the road, the bottle shop was inundated with rats at night amid intense drilling on the project.



In a statement, Sydney Water said it had permission to work only between 8pm and 5am that part of the city, as it was densely populated and near major roads.

"Our noisiest work is done before midnight," the statement read.

Night work on the Refresh Woolloomooloo project has enraged many businesses. ( ABC News: Paige Cockburn )

When Sydney Water announced in 2016 they would build a new pipe just for sewerage, many people were relieved.

"There's no question it needed to be done ... it had been 25 years of stench," said Darlinghurst resident Jane Anderson.

But she described the project as a "nightmare".

"My personal situation is that where my house is located some days there would be day work from 7am to 6pm on one side and then night works from 8pm to 5am on the other side," Ms Anderson said.

"Being kept awake night after night is just unacceptable."

Sydney Water said all work on the project was managed under the Interim Construction Noise Guidelines, which dictate work practices such as acceptable decibel levels and when to use certain equipment.

However, they are not mandatory.

A Sydney Water spokesperson said work on the Refresh Woolloomooloo project complied with noise recommendations and that there were several options available for people to complain.

They also said representatives completed regular audits of work sites to evaluate compliance.