Before water from the Mississippi River reaches faucets in Minneapolis, it is coagulated, flocculated, carbonated, fluoridated, and chlorinated.
In other words, that don't rhyme, the water has to be treated with chemicals that make the tiny things floating in it clump together, making them big enough to get caught in filters. Water also gets dosed with disinfectants that kill other nasty things that can make people sick.
Some of that happens at the city's ultrafiltration plant in Columbia Heights in a room with more than 1000 white, plastic tubes stacked horizontally in rows. Inside each tube are filters that contain thousands of tiny straws made of a high-tech polymer. The water moves slowly through the filters and waste material gets stuck in the thin membrane of the straw.
Ultrafiltration is more effective than the older sand filtration method in removing harmful pathogens from water, according to plant manager Dale Folen. The holes in the membrane of the filters are small enough to capture things that sand can't.
But it's not perfect.
"This is not a do-everything process," he says. "If we know of a spill on the river, there will be times when we just shut off our intakes and we'll let that pass our intakes." The city was moved to build such a system after the city of Milwaukee suffered an outbreak of cryptosporidium in 1993, Folen says. Hundreds of thousands of people were sickened and 100 people died after drinking tainted public water. Cryptosporidium is particularly hard to catch because it's chlorine resistant, Folen says.
One floor below the filters, several large, brightly colored pumps move water at high speeds. The green pumps are pushing unfiltered water up into the filtration room. Once it's done, the filtered water comes back down through this room and flows out to reservoirs and eventually to city water mains.
Each pump is designed to produce between 17 and 20 million gallons per day, which means the plant can produce 70 million gallons of filtered water each day. At that rate, the plant could fill Lake of the Isles in just four days.
The plant produces so much filtered water, the city has something of a surplus, Mayor R.T. Rybak says.
"We've spent a lot to make the water as good as it is. But we haven't done much to tell people about it. Minneapolis is kind of like a company with a product in the storeroom. It's a great product. Every once in a while you need to tell people a little bit about that product in order to move the cases off the shelves."
In 2007, the city dedicated $200,000 towards promoting Minneapolis water to residents and to other municipalities. Golden Valley, New Hope, Crystal, Columbia Heights, Hilltop and parts of Bloomington and Edina buy and use Minneapolis water. They pay a total of around $10 million a year and Rybak would like to see that list expand.
There are other reasons why public water is better than what Rybak calls "plastic water". The plastic bottles are showing up in greater numbers in landfills. Plus, he says, Minneapolis water tastes good.
"The water you drink out of the tap in Minneapolis is great drinking water. And we'll put that up against private, plastic water any day of the week. And in fact, in all these taste tests that are done. We wind up coming off just great."
Several years before the new filtration plant was built, Minneapolis tap water was selected over a couple popular brands of bottled water in a taste test on public radio's The Splendid Table.
Officials at the filtration plant say the taste of Minneapolis water comes from the addition of activated carbon which removes certain odors.