An unmistakable chlorine "pool smell" used to greet swimmers when they arrived the Oxford Community Center in St. Paul, Minn. "Now you don't smell it anymore," said Lynn Waldorf, aquatics director for the City of Saint Paul.
Meanwhile, at the city's outdoor pool, asthma sufferers reported less need for their inhalers last summer due to the reduction of the use of chlorine.
The secret to the pools' new reputation is the same thing that makes the state's northern lakes so clear: The pools now rely on sphagnum moss to clean the water.
The technology was developed by Creative Water Solutions, which is based out of Plymouth, Minn.
"People started stopping me and saying, 'What are you doing? The water is great,'" said Waldorf.
"We kind of make a little mini-bog off of the pool where the water passes through very slowly, and the moss conditions it and enhances it."
Sphagnum moss acts to inhibit the growth of microbes in the pool, says founder and CEO of Creative Water Solutions, David Knighton, who is also a surgeon.
He first became intrigued by sphagnum moss after reading about injured World War I soldiers whose wounds were packed with moss had greater survival than those whose wounds were packed with cotton.
"I knew from my years working with wound healing that it had to be antimicrobial," Knighton said.
His first interest was in medical applications, but Knighton, who is also a pilot, suspected that the moss might be helpful in conditioning water after flying northward over Minnesota's many lakes.
"As I went north, they got cleaner and cleaner," he said. "I wondered: 'Well, maybe it's the moss?'"
Frustrated that he could not keep his home spa chlorine levels stable, he tossed some sterilized moss in. "Within ten days, it cleaned up the spa."
The moss readily absorbs heavy metals, including iron, which often encourages microbial growth. Without any iron in the water, microbes can't grow.
But, more importantly, Knighton says, the moss also prevents the growth of biofilm, mats of bacteria that stick to pool surfaces and coat the inside of pipes, causing corrosion.
Biofilm absorbs the chlorine added to the pool, requiring increasing amounts of chlorine to maintain the required levels in the pool water.
As biofilm disappears from the pool with the use of moss, chlorine requirements decline.
"The moss allows chlorine to do its job," Knighton said. "The amount of chlorine you need decreases by 50 percent."
The Saint Paul outdoor pool saved around $35,000 in chemical costs this summer, Waldorf said. Meanwhile, revenue increased $100,000 as more swimmers visited the pool.
Knighton's business first targeted home spas (hot tubs) and pools. The Saint Paul pools were the first test of the system at a larger scale.
However, this is just the beginning of the applications Knighton has in mind. He is also targeting spa manufacturers, who fill their spas with water for testing in the factory.
Some of the water used in testing remains in the spas, where biofilm forms. This means home spas start out with a dose of biofilm before they're ever used.
Installing moss treatment in the factories could prevent this initial contamination, he said. A trial with one spa manufacturer reduced the initial biofilm load by 95 percent.
Knighton is also testing poultry watering systems to see if treating the water with moss changes the quality of the eggs and meat that result.
He has developed a system for treating home water supplies that has been installed on a trial basis in about 20 homes. "I've had moss in my house for two years, and people think I have bottled water."
Any industry that uses water could potentially benefit from moss treatment. Knighton wants to install his system on the cooling water at a power plant to test its effects on the water there.
For now, Knighton's products are filled with moss from New Zealand, where there is already a sphagnum moss harvesting industry in place. Moss is harvested by hand and flown out by helicopter to prevent damage to the bogs where the moss grows.
Knighton is currently lobbying Minnesota officials to develop regulations for sustainable moss harvest. "Northern Minnesota is the Saudi Arabia of moss," he said.