Pouring water through your nostrils with a neti pot can help relieve symptoms of allergies, colds and flu. But it also could cause illness or even death if used improperly, federal health officials are warning.

Two people in Louisiana died of rare brain infections after they used neti pots filled with tap water contaminated by the amoeba called Naegleria fowleri -- the same amoeba that caused the death of a 9-year-old Stillwater boy Aug. 7 after he swam in Lily Lake. The amoeba enters the nasal passage and moves into the brain, causing a form of meningitis that is almost always fatal.

Even in Minnesota, where cooler water makes the amoeba far more rare than in the South, people with neti pots or other nasal cleansers should use distilled water or tap water that has been filtered or boiled 3 to 5 minutes and then cooled, state and federal officials say. Then the devices should be washed with distilled or boiled water and dried with a paper towel or air-dried.

The amoeba is killed by stomach acid if swallowed, and by the salt water typically suggested for use in neti pots and similar devices. Some untreated tap water is not safe as a nasal rinse because it contains low levels of bacteria and protozoa, including amoebas, the Food and Drug Administration (FDA) said in its recent warning.

"We don't regulate for that particular organism," although water-treatment plants probably will eliminate it with filtration and chemical treatment, said Karla Peterson, who heads the community water supply program at the Minnesota Department of Health. "Still, we recommend you use distilled or boiled water. The risk is low, but it's a risk you don't need to take."

The FDA also warned manufacturers because some devices come with misleading or no directions. It suggested users consult with doctors or pharmacists if directions are not clear.