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From river to tap Exploring how Minneapolis gets its water

Celebrating 150 years of Minneapolis Water Works

By Sarah McKenzie

In 1867, the Minneapolis City Council authorized the establishment of Minneapolis Water Works, a division that initially supplied water to the Minneapolis Fire Department.

The City established its first drinking water pump station by 1872 on the Mississippi River above St. Anthony Falls and expanded its distribution to residents—making Minneapolis the first city in Minnesota with a public drinking water system.

The City's first drinking water pump station.

Today Minneapolis Public Works Water Treatment & Distribution Services has developed a complex system that pumps approximately 21 billion gallons of water each year from the Mississippi River. It produces an average of 57 million gallons of drinking water each day—a rate that could fill Lake of the Isles in about four days.

“I tell people the safest thing in your house—by far—is the water,” said George Kraynick, the City’s water quality manager. “Every drop of water that runs through our facilities is monitored and analyzed 24/7. Our lab operations staff do over 500 tests per day, verifying the safety of the water.”

One of the unique ways the City tests for potential water contaminants is the use of freshwater mussels as part of a pilot project supported by a grant from the U.S. Environmental Protection Agency.

The mussels used in the pilot project.

The mussels can serve as an early warning system and alert water plant operators of potential threats to the water supply since they clam up if they sense a change to their environment. The mussels are outfitted with monitors, which feeds data to a computer that can be monitored by Kraynick and his colleagues.

Overview of water treatment process

Source: The Mississippi River

The Mississippi River is the sole source of water for the city and the surrounding communities also served by the City’s Water Treatment & Distribution Services.

The Mississippi River next to Pump Station 5.

The river water enters the treatment system at Pump Station 5 in Fridley. The river water is screened and then pumped to the Fridley Softening Plant for treatment.

“If you go down to the river, you see all kinds of sticks, leaves and debris,” Kraynick said. “We don’t want any of that stuff coming in so, the bar screens trap the debris on the outside and keep it out.”

Another view of the river from Pump Station 5 -- where water enters the City's treatment system.

The City treats about 57 million gallons a day, which works out to around 700 gallons per second, he said.

Water treatment process

After the water is screened at Pump Station 5, it is pumped to the Fridley Softening Plant. All the water treated by the City flows through this plant and 85 to 90 percent of the treatment process happens there as well.

This is also where lime, aluminum sulfate and carbon are added to the water.

A sample of the lime used to treat the water.

“The river water pH is around an 8 to 8.5. When we add the lime to the water, it raises the pH up to an 11. Taking the pH up to an 11 causes the calcium that’s already in the water to precipitate out of the water,” Kraynick said.

That process softens the water and removes some of the color. To get rid of the rest of the color, aluminum sulfate is added.

“Now we’ve reduced the hardness of the water and gotten rid of the color. The main thing that’s left is taste and odor, which are the most important things to most customers. To get rid of taste and odors, we add powder-activated carbon,” he said. “So basically three chemicals pull out 90 percent of the materials we want to take out of the river water. The remaining 10 percent is what we use disinfection and filtration for.”

The large cones at the Fridley Softening Plant used during the water softening process.

After the softening process, the water heads to two recarbonation chambers, which hold about a million gallons of water each. During the carbonation process, the water’s pH is lowered from an 11 down to an 8.8.

Then the water heads either to the Fridley Filter Plant or the Columbia Heights Membrane Plant.

“From this point on the water is either going to go right next door to the Fridley Filter Plant via Pump Station 6, or it’s going to be gravity fed down to Pump Station 4 by the Camden bridge and then pumped up to Columbia Heights,” Kraynick said. “That’s where we disinfect and filter the water.”

Fridley Filter Plant

The Fridley Filter Plant is in the midst of a major upgrade.

The Fridley Filter Plant, a conventional filtration plant, is being upgraded. This plant can treat about 140 million gallons of water per day.

“What we’re doing right now is feeding powder activated carbon to control taste and orders,” Kraynick said. “When we upgrade the facilities at Fridley Filter, we’re switching from sand and anthracite filter media to sand and granular activated carbon, which removes taste and odors from the water.”

Currently the water goes through a gravity filter, which includes about 30 inches of anthracite coal and about 12 inches of sand. “Its sole purpose is to filter out any particulates left in the water," he said.

A view of the gravity filters.

A number of chemicals are added to the water at the filter plant:

• Chlorine disinfects the water.

• Ammonia stabilizes the chlorine.

• Ferric chloride/polymer removes any remaining particulate matter so it can be filtered.

• Ortho/poly phosphate is added for lead and copper corrosion control.

• Fluoride is added for dental health as required by state law.

• Sodium hydroxide is added as the final pH adjustment.

Water then passes through two 16 million gallon reservoirs where pumps distribute finished water to Minneapolis and the Columbia Heights reservoirs.

Columbia Heights Campus

The Columbia Heights Membrane Plant has a chemical process similar to the Fridley plant’s, but the water goes through ultrafiltration membranes rather than gravity filters.

The Columbia Heights Ultrafiltration Membrane Plant.

The membrane plant can produce 70 million gallons of drinking water per day.

A pipe carrying water that has finished the ultrafiltration process.

After the water leaves the plant, it is pumped into reservoirs.

The whole process—from when water enters the system from the Mississippi, goes through the treatment process, gets distributed and then makes its way to your tap—takes more than a day.

Distribution

The City provides drinking water for roughly 500,000 people, including suburban customers in Golden Valley, Crystal, New Hope, Columbia Heights, Hilltop, New Brighton, Edina’s Morningside neighborhood and Bloomington.

An illustration of how water is connected to properties via the water main.

After leaving the reservoirs, the water is pumped into an extensive network of underground piping. Water from the water mains under the streets is connected to properties via service lines, which connect to your faucets, and voila, it’s time to enjoy a nice glass of Minneapolis water.

Minneapolis water fresh from the tap.

Before and after

Before and after: River water and finished water after its gone through the City's treatment process.

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