An upgraded sewer system in South Shore has now been connected up and is in operation.
United Utilities completed the work to its deadline of the end of April for the scheme which includes a new pumping station on land off Midgeland Road.
The investment is part of a £35m project to update an 80-year-old waterworks system which had been struggling to cope during times of heavy rainfall.
New pipes have been laid under routes including Highfield Road and Midgeland Road, existing pumping stations including Lennox Gate have been upgraded and an underground holding tank has been built at Fishers Field to capture stormwater.
The investment will mean cleaner bathing water by reducing the amount of rainwater which gets into the sewers.
Rainwater does not need to be cleaned, so removing it leaves more room for dirty water from toilets, showers and sinks which can be sent off for treatment.
This in turn reduces the risk of sewage backing up during times of heavy rain and prevents polluted water going into the sea at times of overflow.
Some traffic restrictions will remain in place while work is done to reinstate roads and grassed areas.
This is expected to take another couple of months to complete.
Steve Wong, area stakeholder manager for United Utilities, said: "The pipes have now been connected up and the pumping station on Midgeland Road is working.
"The Fishers Field storage tank is also in operation.
"We are now tidying up and there is a lot of reinstatement of the roads to be done.