An environmental group in Halifax is questioning a request from Halifax Water to shut off a part of its sewage treatment systems for the winter.

The treatment plants in Halifax, Dartmouth, Herring Cove and Eastern Passage use an ultraviolet system on the sewage before the water is sent into the harbour. The process reduces the levels of bacteria.

The ultraviolet system uses a lot of electricity and Halifax Water says turning that system off for part of the year and practising seasonal disinfection will save money and reduce greenhouse gas emissions.

James Campbell, a spokesman with Halifax Water, said turning the system off between November and April is not unheard of.

"It's quite common right across the country," he said. "Either salt water or fresh water and also right up and down the Eastern Seaboard of the U.S. It's not an uncommon practice at all."

Campbell said the move could save $1,000 a day and significantly reduce greenhouse gas emissions, but it would increase bacterial levels in the harbour.

"There'd be no change in the clarity of the water, the full treatment process is still going on," he said.

"You'd still have screening of all the floatables, there'd be no smell in the harbour so there'd be no visible or odour-related issues related to this at all. It's strictly a cost-saving measure."

Campbell also pointed out not many people use the harbour for recreation in the winter.

Jocelyne Rankin, the water co-ordinator for the Ecology Action Centre, is not convinced.

"It was a significant impact by Halifax taxpayers and so to reduce the scale of it is questionable," she said.

"We have a lot of pharmaceuticals in our waste water. UV disinfection can have some effect on eliminating those drugs, so if we're cutting out the UV disinfection those drugs can still have an effect on the environment."

Rankin said treatment systems around the world are being upgraded and not scaled back.

The public has until Feb. 20 send in their comments on the proposal. The proposal then needs the approval of Nova Scotia's Environment Department before it can be implemented.