Several Twin Cities suburbs are warning residents to be on the lookout for an apparent scam in which homeowners are asked to spend thousands of dollars on unnecessary water-filtration systems.

In the past month, plastic bags containing small bottles and a card asking for personal information have been hung from doorknobs in Richfield, St. Louis Park, Edina and Falcon Heights. The card, which bears no company name, website or other contact information, asks residents to fill out a form and leave a water sample to be picked up.

After receiving dozens of complaints, city officials reminded residents that cities test their own water and advised them to ignore such come-ons, especially when they ask intrusive personal questions.

"If you don't see the St. Louis Park logo on there, don't pay attention to it," said Scott E. Anderson, the city's superintendent of utilities.

Minnesota cities are required to send water-quality reports to residents once a year. Cities also regularly test their water. For example, Edina tests its water daily, and Richfield tests each week.

High-pressure sales

After a Richfield resident provided a water sample, a man returned with a "water report" and a high-pressure sales pitch for a $6,000 filtration system, police say. The man asked to use the bathroom, ran water taps around the house and asked for some money upfront, but would not provide a business card or company name. The man was in the house for about 45 minutes, and the resident had trouble getting him to leave.

"He wouldn't leave," said Police Lt. Mike Flaherty. "He kept pressuring. ... People involved with scams can be very convincing."

When the man finally left, the resident notified police and the city about the visit. They could not locate the man's gray and white sedan.

Work, income info sought

Robert Hintgen, Richfield's utilities superintendent, said his department has received dozens of phone calls about water testing from confused residents.

Some wondered if the bags were left by the city or if city officials knew what the testing was about. Many were suspicious because the card asked for personal information, including whether recipients worked and what their income was.

Hintgen advised residents to ignore the bags. "If people want their water tested, we'll do it for free," he said.

Arona Street in Falcon Heights and parts of Edina and St. Louis Park were hit with similar solicitations before Thanksgiving.

Ben Wogsland, spokesman for the Minnesota attorney general's office, said privacy laws prevent the office from revealing whether anyone has complained about the water-filtration solicitations.

"If people do have complaints, we would certainly want to take a look at them," he said.

Mary Jane Smetanka • 612-673-7380 Twitter: @smetan