Students from Waratah Public's Before and After School Care OSHClub were evacuated on Tuesday afternoon due to a wastewater overflow that created a blockage.

A spokesperson for Hunter Water confirmed on Wednesday that plumbing works had been completed.

"Our crews were there yesterday to clear the blockage and then clean and disinfect the area, which was fenced off for safety," the spokesperson said.

"We're informed the Department of Education and there won't be any impact to kids attending school today."

Parents were contacted around 4.30pm on Tuesday and asked to collect their children from Waratah's OSHClub.

In a text message, parents with children at the school were told: "It has been brought to our attention by the school that there is an urgent plumbing issue that requires immediate rectification works to commence.

"It has been requested that families collect child/ren from OSHClub as soon as practical."

Meanwhile, Hunter Water has announced it is investing more than $10 million to upgrade the Toronto Wastewater Treatment Works (WWTW) to reliably meet local population growth, reduce odour and protect the environment.

A state-of-the-art odour control unit (OCU) at the facility has been installed and is operating.

The upgrade began in 2021 and is expected to be complete by this winter.

Hunter Water executive manager customer delivery, Glen Robinson, said the upgrades will provide lasting benefits to the community.

"These upgrades to Toronto WWTW, in particular, the new state-of-the-art odour control unit, will significantly improve the capture and treatment of wastewater-related odours," Robinson said.

"As a business, we're doing everything we can to minimise community impact from our assets - particularly odours," Mr Robinson said.