Brent Walden turns on the taps as soon as he walks into the pumphouse, making sure that the lines have been flushed clean before he takes a water sample. A systems maintenance operator with the city, he spends about a day a week testing the city's water supply, sampling water in the north end of the city one week, and the southern end the next.

Today he will collect water samples from a range of sites, including the Lion's pool, Vanier school and City Hall. But it is the tests taken here in the Selkirk Street Pumphouse that clearly show the water purification system at work.

The pumphouse is located in Riverdale near the edge of the Yukon River. Water from Schwatka Lake and the ground water wells is chlorinated here before beginning its trip through the complicated maze of pipes, pumping stations and other paraphernalia that make up the city's water supply system.

Walden takes samples from both the untreated water and from a tap with chlorinated water. The samples will be labeled, wrapped in bubblewrap, and within hours they will be mailed priority post to an accredited lab in British Columbia. There they will be tested for both total and faecal coliform bacteria.

Many coliform bacteria are perfectly harmless to humans, and are regularly found in the untreated water. In almost half of the tests taken in 1999, for example, concentrations of total coliforms in the untreated water exceed levels set out in the "Guidelines for Canadian Drinking Water Quality," a voluntary set of national guidelines.

Faecal coliforms are of much greater concern. These bacteria come from human and animal wastes, and can be deadly. Seven people were killed in Walkerton, Ontario, after drinking water contaminated with a particularly bad strain of coliforms called Escherichia or E. coli.

This time of year there should not be many coliforms in the water. Levels typically rise in the spring and summer when there are more animals moving about and sediments are washed into the surface water by spring runoff and rain.

Faecal coliforms were found in the untreated water from Schwatka Lake in about one-third of the 1999 tests. These results mean that you probably do not want to drink water straight from the Yukon River, but it does mean that water must be chlorinated to ensure that the water coming out of your tap is safe to drink.

In Whitehorse, the main line of defence against all waterborne disease is in the room next door, where tanks of chlorine gas are stored. Chlorine is injected into the untreated water before it is pumped through the distribution system. To ensure that chlorine is always added to the water supply, the water pumping system shuts down if the chlorine system fails.

Walden has been collecting these samples for about 15 years, and says that he has never had a bad sample of chlorinated water in that time. He is a certified wastewater operator and regularly gives tours of the system to school groups and other interested parties.

Chlorine does not always kill giardia, a tiny microorganism that can cause the gastro-intestinal disease giardiasis. Commonly known as "beaver fever," giardiasis can cause cramps, nausea and diarrhea. It can be treated with prescription drugs, but will usually clear up on its own in healthy people.

"Giardia is a hard thing to get rid of," says Walden. "It hides in the dirt particles, so the chlorine gets used up by the dirt."

Larry Shipman, an engineering technologist with the City, is responsible for reviewing the water test results. He says that giardia has never been a big issue in Whitehorse as levels are very low in the untreated water, particularly when compared to other Canadian cities.

But the City is considering other water treatment options. When it rebuilds the aging pumphouse in 2012, a contact chamber will be installed, in which the chlorine will have more time to mix with the untreated water and kill the giardia. A filtration system may also be considered, though city officials do not think it is needed at this time.

"Filtration will reduce the number of giardia cysts, but it does not completely get rid of them," says Shipman.

Municipalities with high concentrations of giardia will use both filtration and chlorination to reduce the number of cysts. Chlorine can kill giardia cysts if it is in contact with them for a long enough time, and there is not too much sediment in the water.

The City tests for giardia regularly and public health officials also monitor the reported infection rates to make sure that the City's drinking water is not causing problems.

Walden does not do the giardia testing. Once a month a private contractor takes those samples. The City also tests twice a year for things such as metals, pH, and turbidity.

But it is the coliform tests that are the core of the water quality program. The Yukon's Medical Officer of Health first receives the results of the lab tests, and would notify the City right away if any worrisome results were reported.

Walden will also test the water in people's homes if they request it. After the deaths in Walkerton, the number of these requests shot way up. He always suggests that people clean the filter in their taps, or just get rid of it altogether, as this provides a place for bacteria to breed.

Today, after the pumphouse, his next sampling stop is Well Number Six, one of the City's five groundwater wells. After that it is on to the Vanier Catholic Secondary School, where he always takes samples from the same tap in the same men's washroom, just to make it easier to track problems if they do occur.

Walden says that the system for water testing is much more formalized now than it was when he started working for the City fifteen years ago. Now the City is considering other changes such as testing all of the sites once a week, and continuing to test at the schools even in summer when they are closed.

Like every water system operator in Canada, he knows that there is more public interest now in how the water purification system works.

"We have never had bad water but because of Walkerton, we have talked about revamping our testing program," says Walden. "But our water is fairly safe. There is no large industry here."

For more information on the City water supply, contact the City Engineering Department at at 668-8305.