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A Canadian water purification company is using some questionable tactics to make people think their tap water is dirty, CBC's Marketplace has learned.

Maggie Karpouzos, a small business owner in southwestern Ontario, agreed to a free in-home test of her tap water last year.

"We were under the impression they were going to test the water, there was something wrong with it — they are from the city of London," she said. "We had no idea they were trying to sell us something."

Clean water, dirty tricks

Watch the full Marketplace story on the show's website.

The salesman was not a city employee – he was selling a water purification system called Simple H20 that costs thousands of dollars.

CBC's Tom Harrington showed a testing kit used by a Simple H20 distributor to Dan Huggins, the City of London's water quality manager.

Inside the kit, he found chemical drops that interact with water to make it look cloudy, dirty and undrinkable.

"They've used a little bit of chemical trickery to make it appear that there are these hidden contaminants in tap water, and it's simply not the case."

Marketplace's investigation also uncovered a sales pitch laced with scary warnings about chlorine in drinking water.

Colin Mackenzie, who works with Ontario's Ministry of Consumer Services, said these companies might be breaking the rules.

"False, misleading presentations were made and that's an unfair practice, which is an offence under our consumer protection act," he said.

The distributors who sell these systems say they're trained at Simple H2O's head office in Woodbridge, Ont. The company president told Marketplace he was too busy to do an interview.