Clean drinking water is something almost everyone — at least in the United States — takes for granted. Turn on the tap and it's there.

But few people know exactly where it comes from and the elaborate steps most cities take to make sure it's clean and safe.

Apple Valley last month completed a $15 million expansion of its Water Treatment Facility and maintenance campus and about 250 people showed up at a July 25 open house to climb on snowplows and explore the huge new concrete utility garage and vehicle wash bay.

The treatment facility, which provides water to the city's almost 50,000 residents, didn't lack capacity, the city simply wanted to be able to accommodate future growth, said acting public works director Colin Manson.

Utility supervisor Carol Blommel Johnson led a tour of the facility last week and explained how it works:

Apple Valley routinely uses 15 wells, each sunk 450- to 480-feet deep into the Jordan aquifer, which runs under parts of Minnesota, Iowa, Illinois and Michigan. Another five wells provide emergency backup.

The water flows into the treatment plant via a huge vertical mint-green pipe, then into a concrete reservoir the size of a tiny bathroom. There, sodium permanganate and the first dose of chlorine are added to aerate and oxygenate the water, which is then sent three ways to 12 filter cells.

The plant, monitored and run almost entirely by computer, theoretically can produce 24 million gallons of drinking water per day. It typically it produces 4 million gallons a day in the winter and up to 16 million gallons a day in the summer months.

Why does the need quadruple in the summer months?

"Lawn irrigation," Blommel Johnson said. "People washing cars. Kids playing in the sprinkler. You're doing more activities outside."

This summer, with plentiful rain, the production is about 8 million gallons per day, she said.

People use 85 to 100 gallons of water per person per day, she said. Many of those are "hidden" uses, such as laundry, cooking, washing dishes, flushing toilets.

Filtering and testing

The filter cells filter iron and manganese from the water. The iron and manganese flow into backwash tanks; when those tanks are filled, a computerized meter reverses the flow of water, freeing the solids, which are then piped into the sanitary sewer system.

Before the water goes into water towers and reservoirs, chlorine (to kill any harmful bacteria) and fluoride (for dental health) are added.

Tests are done daily and weekly to make sure the chemical composition is correct and no bacteria is present.

From the plant, giant royal-blue pipes take the clean water to the city's five water towers or a holding reservoir. From there, it's piped into homes.

"The water pressure in your house is a factor of the elevation of the house and the level of water in the water tower," Blommel Johnson said.

The expansion project added four filter cells to the eight already at the treatment plant, two backwash tanks, upgrades to the computer control system and the installation of a dehumidification system to increase the life of the equipment.

City practices vary

Rosemount doesn't have a water treatment plant, but adds chlorine and fluoride directly to each of its eight wells.

Burnsville uses 17 wells and two "surface water" sources, such as quarries for its drinking water. It also filters out iron and manganese. So does Eagan, with 21 wells, and Lakeville.

Although Hastings gets its water from the Jordan aquifer, as do the others, the plant there treats the water from two of its six wells to reduce nitrates. The water doesn't need disinfection with chlorine nor does it contain significant amounts of iron or manganese, city officials said.

All of the water meets Minnesota Health Department standards and each city provides a yearly water quality report on its website.