Wichita ? A musty smell has lingered in the city’s water supply since October, and city officials are turning to ozone gas as a possible remedy.

During the next 30 days, the city plans to experiment with adding ozone gas to the water supply. Ozone, produced by zapping medical-grade oxygen with electricity, is pumped into the drinking water to remove impurities.

If it helps reduce the odor, the Wichita City Council will decide whether to spend $2.1 million a year to regularly treat the water. The cost — about $1 a month for a typical family — would be passed on to residents.

“The $1 a month is pretty small,” said Wichita resident Lorrain Hird, who put a filtration system on her faucet to eliminate the odor, which she described as being like dirt.

The odor in the Cheney Reservoir normally lasts for a few days once or twice each summer. Despite the smell, the water is safe to drink, said David Warren, director of the city’s water and sewer department.

The latest episode began in October and has lasted more than three months. This is the first time the city has had an odor problem in its water during the winter.

“It could go on for a week. It could go on for a month,” Warren said. “It could stop tomorrow. The frustration is that you can’t predict when it will start and when it will end.”

The city suspects the odor is caused by blue-green algae, called cyanobacteria, fed by fertilizer and manure building up in Cheney Reservoir.

Until now, the city has focused on long-term remedies to deal with the algae. Since 1994, Wichita has been working with area farmers to move feedlots and to terrace fields to reduce the chemicals washing into the lake. But it could be years before the efforts pay off, and some residents want the problem solved now.

Warren suspects eight inches of rain in October might have flushed more phosphorous, a fertilizer component and the algae’s favorite snack food, into the reservoir.

Val Smith, an ecologist at Kansas University who is studying Wichita’s water woes, said that because no water has been released from the Cheney Reservoir since July 2001, phosphorous levels may have built up.

To make sure algae are the culprit, the city is shipping three months’ worth of preserved water samples to the university for testing.

In Kansas, about five water supply lakes are prone to blue-green algae blooms, according to Ed Carney of the Kansas Department of Health and Environment.

Winfield, Olathe and Alma all get complaints.

In Lawrence, the blue-green algae got so bad in 1995 and 1996 that the city stopped taking water out of Clinton Reservoir.

So far, only one city in Kansas has solved its taste and odor problems: Emporia, which installed ozone technology about eight years ago.

Since Emporia added ozone to its water, odor complaints have stopped, although the extra oxygen sometimes gives the water a milky-white appearance that some residents don’t care for.