Homeowners are concerned the stormwater system cannot cope with the large number of medium-density buildings planned to be built over the next 12 months.

Twenty-one two and three-bedroom dwellings were approved for the one lot last month on Warners Bay Road, while another 19 two and three-storey townhouses on Cowmeadow Road are awaiting approval by Lake Macquarie council.

The two developments touch boundaries on the downward slope of the hill and share fencelines with another 41 aged care villas, which were built in the 2000s.

Ada Street resident Robyn Single said she was gobsmacked when she learnt more medium-density housing was planned for the area.

She said her property already took in run-off from Alexander Street, Wilson Road, Warners Bay Road, Cowmeadow Road, as well as parts of Tennent Road and Bayview Street.

When it rains, sewage pipes in her backyard are unable to cope with the influx of water and overflow.

For more than a decade, Mrs Single has been battling Lake Macquarie council and Hunter Water to alleviate the flooding problems on her property.

Due to regular flooding her home's support beams have rusted, the floorboards have deteriorated and rising damp and mould have set in.

A spokesperson for Hunter Water said it had twice visited the Ada Street property to help resolve its flooding issues.

"On one of those occasions Lake Macquarie City Council staff also attended and agreed that the council-owned stormwater infrastructure was causing the flooding at the rear of the property, which had the effect of then inundating the property's sewer overflow gully," the spokesperson said.

Hunter Water subsequently installed a new type of cover on the property's sewer overflow gully to limit the ability of stormwater infiltrating sewer pipes.

Through an investigation in July, Hunter Water found seven properties in Mount Hutton had illegally connected their sewerage to the stormwater system.

Defect notices were issued to the property owners and the illegal connections have now been rectified.

In letters obtained by The Star, the council said drainage on Ada Street was "being investigated" on four separate occasions, dating from 2002.

In a statement issued last week, the council said Ada Street was part of a current "drainage study" that covers the greater Charlestown area.