Winnipeggers are holding their noses yet again to fend off the distinctive musty smell and taste that often plague the city's tap water in the summer.

Winnipeg's water has an odd taste for a few weeks almost every year due to seasonal algae growth in Shoal Lake, a 227-square-kilometre lake on the Manitoba-Ontario border that provides Winnipeg's drinking water.

Despite its unpleasant taste and smell, Winnipeg tap water is still safe to drink, says Winnipeg Regional Health Authority's medical officer of health. Tap water is routinely tested during the summer season for substances produced by algae.

"Residents can continue to use the water, and there is no need to take special precautions," said Dr. Margaret Fast in a release.

Water filters and devices with the certification "ANSI/NSF Standard No. 42 for the reduction of taste and odour" can help make the water more palatable, city officials said.

However, the algae also causes home water-treatment devices, strainers and aerators to plug more frequently. A build-up of sediment could also occur in hot-water tanks.

The algae could be a factor until late fall, city officials said.

Water-treatment plant should help

Diane Sacher, manager of the city's water services, said a new water treatment plant, expected to come online in 2009, should help solve the problem.

"In addition to allowing us to meet drinking water quality guidelines, the water treatment plant we're building will also reduce odour levels and improve the taste and appearance of our water," she said.

Water from Shoal Lake has been piped to Winnipeg through a 135-kilometre aqueduct for nearly 90 years.

Once the water arrives in Winnipeg, it is stored in the Deacon Reservoir, which can hold 8.8 billion litres — enough water to supply Winnipeg for about 20 days, city officials estimate.

The city uses chlorination to disinfect the water, adding it at Shoal Lake, the Deacon Reservoir and at the pumping station that serves each neighbourhood.

Fluoride is also added to prevent tooth decay, as well as orthophosphate — in the form of food-grade phosphoric acid — to reduce exposure to lead through the corrosion of lead pipes.