"Empowered water" sounds like a product sold by door-to-door salesmen and in late-night infomercials. It's the key ingredient in Zerorez carpet cleaning, but in simpler terms, it's softened water whose ions have been scrambled in electric current. Without the soapy residue that can quickly attract dirt after a cleaning, carpets stay cleaner longer, said Michael Kaplan, manager of the Twin Cities franchise.

But is it green? That's a buzzword that Zerorez has adopted, as have other Twin Cities carpet cleaners such as GreenClean, Amazing Green, MN Green Clean and Mr. Green Clean. Most of them use soap derived from plants rather than chemicals. GreenClean uses nontoxic extracts from grapefruit and orange peels called Bioclean.

But being green goes deeper than the cleaning agents. It's also the equipment and water disposal, said Alan Srbich of CarpetClean in Blaine. "No one cleans totally green," said Srbich, "but we try to be environmentally friendly."

That could mean using smaller trucks and equipment that runs at lower revolutions per minute to put less carbon into the atmosphere. The wastewater should be disposed of in a sanitary sewer that is treated (similar to sewage), not into a street storm sewer that runs unfiltered into streams and rivers, he said.

Evaluating a green carpet cleaning company is like buying organic produce or meat. Many local farmers don't sell "certified organic" meat or produce because they can't afford the certification process, but a consumer can find out which guidelines a grower follows by asking a lot of questions at the farmer's market. In the cleaning biz, the Green Seal (www.greenseal.org) is one certification company to look for. Fridley-based GreenClean is considering the certification, but at a cost of $10,000 per year it's a high price for a small business, said co-owner Jason Schroeck.

I decided to try Zerorez and GreenClean myself to evaluate how well a green company cleans. In the past I have used CarpetClean and Sebastian's Carpet Care, both top-rated by Twin Cities Consumers' Checkbook or Angie's List. Both of those companies returned for a second visit (at no additional cost) when certain stains weren't removed.

None of the four companies are dirt cheap, but I gave up on the "$6 per room" cleaners years ago after poor dirt removal, long drying times and multiple add-on incidentals jacked up the price. I expected green companies to be higher priced than the highly rated traditional carpet cleaners I've used in the past, but they're not. Expect to pay $150 to $300 for most homes.

I gave Zerorez the easier job -- a set of stairs with minimal wear and dirt and a large room with a couple of stains and dirty high-traffic areas on ivory-colored nylon carpet. The cleaning was as good as any other company I've used. Zerorez removed a spot that the two previous cleaners couldn't. One dirty, high-traffic area still looked gray after drying. When I asked them to clean the spot again, it was much improved. The cleaner suspected that he may have accidentally missed the area the first time around. Zerorez left no odor except for a damp smell while the carpet was still wet. It dried quickly because the company brought high-volume fans to speed the process (no extra charge).

The total bill was relatively low, due to a winter special still in effect ($143 for three rooms, normally $173).

Winter is a slow time for carpet cleaners, which makes deals more likely. I prefer to get my carpets cleaned when it's cold and the humidity is low. Carpets dry slower in high humidity, which can be an inconvenience at best (stay off until dry) and mold-inducing at worst. As a rule of thumb, the more fans you can use to dry the carpet quickly, the better. Ask carpet cleaners to bring their own high-powered fans but set out your own, too. Have the cleaners start them when they're done so you don't have to walk on wet carpet. You can also ask them to do an extra extraction to remove even more water.

GreenClean got the tougher job -- ivory olefin berber in the basement with traffic dirt on the stairs, multiple hairball stains from my cat, Thelma, and one old urine stain from my other cat, Floyd. Most of the cleaning was a big success. The hairball stains vanished. The urine stain, although still visible, was cleaned and deodorized better than any previous attempts.

The only disappointment was a lingering fragrance. GreenClean said this was the masking fragrance that was used on the urine spot, not the entire carpet. To be fair, the fragrance would not be used in standard cleaning, and it was gone after a couple of days.

Another issue that came up was not GreenClean's fault. Previous cleanings from other companies have been difficult because my light-colored olefin carpet "browns" easily, leaving tan streaks in the carpet after cleaning. If the carpet dries quickly, the browning is minimized. With GreenClean I used several fans to combat it, but there was still minor browning. A good carpet cleaner will be able to get rid of browning easily without additional cost, which GreenClean did. GreenClean was a little more expensive ($169) than Zerorez for about the same square footage.

I would rate both companies as excellent. Both get an "A" rating from Angie's List, although Zerorez (952-937-6739, www.zerorezmn.com) has been rated by more customers. In 2009 GreenClean (763-789-9600, www.greencleancare.com) received Minnesota's Better Business Bureau Integrity Award for delivering quality, eco-friendly cleaning and water restoration service. For more service providers, search Google for "green carpet cleaners Minnesota."

John Ewoldt • 612-673-7633 or jewoldt@startribune.com. If you spot a deal, share it at www.startribune.com/blogs/dealspotter.