Minnesotans are spending millions of dollars to deal with nitrate contamination in their water, and the state agriculture department says it's time to insist that farmers do more to prevent the problem.

Critics say regulators have moved too slowly as the problem worsens, but the Department of Agriculture says it plans to use a new set of rules to be more aggressive in getting farmers to do things that limit the amount of fertilizer chemicals leaching into groundwater.

Groundwater is the state's main drinking water source, and the department estimates the aquifers beneath 10 percent of the state's land have nitrate problems.

Nitrates are a groundwater pollutant that can come from several sources. They occur naturally in the soil as part of the growth and decomposition of crops, but farming contributes to the problem through the nitrogen fertilizer applied to fields, mainly for the state's largest crop, corn.

At high concentrations in drinking water, nitrates can pose health problems, particularly for babies. What is known as blue baby syndrome can be fatal.

The problem has been known for decades, and state regulators long have had rules aimed at encouraging farmers voluntarily to take steps that cut the amount of nitrate reaching drinking water sources. Now they are revamping those rules.

Assistant agriculture department commissioner Matt Wohlman said the agriculture department plans to be more aggressive. That may include forcing some farmers to change, he said. "We could restrict how much nitrogen is applied," said Wohlman. "We could restrict the timing, the source, the placement of those products. We could also require certain best management practices be put in place."

The department hasn't moved fast enough or forcefully enough, said Kris Sigford, water quality director at the Minnesota Center for Environmental Advocacy.

"Unfortunately, we have a bigger environmental problem than we had a quarter of a century ago," said Sigford. "It's time to move from purely voluntary to regulatory, to develop some practices that actually work and require them to be employed in certain regions of the state."

Tim Figge is one of the Minnesotans who has had to pay for the problem.

For years, the rural Hastings residential appraiser had little concern about his household water, drinking it straight from the well.

But that changed two years ago, when one of his daughters, pregnant at the time, came home for a visit. Figge knew some of his neighbors were having trouble with rising nitrate levels in their wells. He also knew they could be a health threat for expectant mothers and young children. So he had the local creamery run a $12 test for nitrates."

The results showed unsafe levels of nitrates. Figge bought bottled water for his daughter's visit but he also got to wondering why groundwater nitrate levels were increasing in his neighborhood.

"You can feel it," Figge said, digging up a shovelful of soil in his yard. "It's really sandy. And that's the problem."

Because the soil in his part of Dakota County is sandy, surface water drains quickly from the surface. It picks up nitrates, quickly carrying them into the aquifers that supply Figge's drinking water.

Denser soils tend to hold back nitrates. But in this area, sandy soil is common, and that's leading to a growing spate of drinking water problems. Last summer Dakota County tested more than 700 wells.

"Unfortunately the results were much worse than we were expecting," said Jill Trescott, the county's groundwater protection supervisor. About a third of the tested wells had nitrate levels that are unsafe, she said.

"Where it's at such a high level that it's causing problems, it does seem to be very strongly associated with row crops," Trescott said.

Figge spent $700 for a reverse osmosis system to reduce the level of nitrates in his water.

Residents elsewhere are paying, too. Hastings, St. Peter, Lincoln Pipestone Rural Water and other public and private entities have spent tens of millions of dollars installing equipment and taking other steps to make water safe to drink. Most often consumers pay the cost of the cleanup through higher water bills.

The state's agriculture department, the main agency responsible for regulating nitrates, estimates about 280 townships - one-tenth of the state's area -- have problems with the chemical in groundwater.

Sigford points to department data that show a growing rate of nitrate contamination in six of seven testing regions over the past quarter century. From 1985 to 1999, two-thirds of water tests in those areas showed nitrates; from 2000 to 2010, nine out of 10 did. Unsafe concentrations rose as well.

To Sigford, that's a clear signal of policy failure, proof that the nitrate problem is worsening.

Assistant commissioner Wohlman disagreed. While the data suggest an increase, the department's findings aren't detailed enough to draw a firm conclusion, he said. "We do believe that nitrogen in groundwater is a major issue for the state," he said. "The data is not deep."

The department has long had the authority to require farmers to make changes in their practices to limit nitrates in groundwater. But Wohlman said he wasn't aware of any time regulators have used that power.

He said that in the past there hasn't been enough state money to support mandatory action. And he said it's not clear why nitrate levels may have risen. Nitrates exist naturally in soil, whether fertilizer is applied or not.

But he said even though voluntary changes by farmers will remain the centerpiece of the department's strategy on nitrates, agriculture regulators will become more forceful.

The agency plans, for example, to ban fall application of nitrogen fertilizer in parts of the state.

Another step underway is the agriculture department's plan to test 70,000 water wells across the state for nitrate contamination.

Naturally, Minnesota farmers are closely following the debate over how best to manage nitrates. Many farmers - no one knows the number exactly -- are already taking action to lower nitrates.

"I think it's a very important issue," said Dean Tofteland, who farms four miles south of Luverne in southwestern Minnesota. Tofteland tests the soil on his farm regularly to help him figure more precisely exactly how much fertilizer the crop needs. "Give the crop just enough nitrogen to make a good yield, but not too much where we could lose it," said Tofteland.

That leaves fewer unabsorbed nitrates that can pollute water, he said. He also uses products that delay the conversion of nitrogen fertilizer into nitrates, which also reduces potential pollution.

Besides helping the environment, he said his strategy can boost profits by reducing the amount of money he spends on fertilizer. "It's a win-win in our case," said Tofteland.

One of the difficulties in dealing with nitrate contamination is the time likely needed to generate results. No one knows long it would take for different farm practices to have a measurable impact on groundwater.

But homeowner Figge figures it could only be good news if more farmers did what Tofteland does. "We're edging towards the precipice right now," Figge. said "With high, high levels of nitrates that need to be addressed."