Nitrates and nitrites have become a concern in areas with excessive agricultural runoff or septic system use. Nitrate (NO3) is a tasteless, odorless, and colorless naturally occurring chemical. They are most commonly used as fertilizer and can enter our drinking water through agriculture runoff, leaking from septic tanks, sewage, and erosion of natural deposits.
The EPA defines Nitrates as “nitrogen-oxygen chemical units which combine with various organic and inorganic compounds.”  Nitrates are most dangerous to infants six months and younger, and can cause serious illness and even death if their drinking water exceeds the maximum contaminant level (MCL) of 10 mg/L or 10 ppm. The symptoms can include shortness of breath and “blue baby syndrome.”
Be especially cautious of your water quality if you live in an area with lots of agricultural fertilizer runoff or excessive septic systems, it is recommended that you test your water every two to three years. Most likely you will be notified by your water supplier if your drinking water exceeds the MCL, but if your water comes from a well, you might consider checking with your health department about local ground water uses and information on contaminants of concern in your area. According to the Minnesota Department of Health, the kinds of wells most vulnerable to nitrate contamination include shallow wells, dug wells with casing that is not watertight, and wells with damaged, leaking casing or fittings. 
Ion exchange, reverse osmosis, and electrodialysis are all effective ways of treating nitrates below 10 ppm, but extreme caution must be used, if not totally avoided, for infants six months and younger.