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  • David Smyth

Nitrates in Drinking Water

Updated: Nov 18, 2022

What are nitrates?

Nitrates and nitrites are compounds that are formed naturally when nitrogen combines with oxygen or ozone. Nitrogen is essential for life, and nitrates are the primary source of nitrogen in plants.

Vegetable and fruits make up for an average of 80% nitrate consumption in humans, and may be beneficial at normal levels, especially when paired with foods high in vitamin C. Vitamin C helps reduce the conversion of nitrates into more harmful nitrites in the blood stream. Processed meats such as sausage, bacon and hot dogs, are also a source of nitrates.

Nitrates may also be found in drinking water. At excessive concentrations, nitrates in drinking water can pose a health hazard, especially to infants and pregnant women.

How do nitrates get in drinking water?

Nitrates can occur naturally in groundwater, typically at low levels. Elevated levels of nitrates occur in groundwater from runoff of nitrogen fertilizers, septic systems, wastewater treatment effluent, animal wastes, industrial wastes, and food processing wastes. Over the past 50 years, human activity has doubled the rate of nitrogen in the ground.

Both municipal and well water may be vulnerable to contamination. Well water may have high nitrate contamination if the well is improperly constructed or the well is located near a septic system or agricultural runoff. Well water may be more vulnerable to contamination after flooding, particularly if wells are shallow, have been dug or bored, or have been submerged by floodwater for long periods.

What are the health effects of nitrate exposure in drinking water?

The Environmental Protection Agency (EPA) has set a maximum contaminant level (MCL) of 10 parts per million for nitrate in drinking water. Nitrate levels above the MCL may present a serious health risk for infants and pregnant or nursing women. While adults receive more nitrates from food, infants receive greater exposure from drinking water because most of their food is in liquid form. Of particular concern are bottle-fed infants whose formula is reconstituted with drinking water contaminated with nitrates. Nitrates can interfere with blood’s ability to carry oxygen in infants of six months or younger. The resulting illness is called methemoglobinemia, or “blue baby syndrome”.

Pregnant women may be less able to tolerate nitrate. In addition, nitrates consumed by nursing mothers may affect infants directly. Pregnant or nursing mothers should not consume water containing more than 10 ppm nitrate directly, added to food products, or beverages (especially in baby formula).

Short-term exposure to high levels of nitrates can cause nausea (upset stomach), diarrhea, vomiting, dizziness, blurred vision, breathing problems and eventually muscle paralysis.

Long-term health effects of drinking water with elevated nitrate levels is not well known. Some research indicates excessive long-term exposure to nitrates may play a role in prenatal problems, birth defects, and a broad range of health disorders.

How to remove nitrates from drinking water?

Municipal water suppliers are required by law to conform to EPA standards for maximum safe levels of nitrates. However, not all water suppliers conform to EPA standards. Be sure to verify your water supply is safe. If your municipal water has elevated levels of nitrates, you may have to contact your state health agency or the EPA.

Well-water owners are not required to test their water. However, it is recommended to test water annually to determine if nitrate levels are a concern.

Avoid drinking water or preparing food with water containing elevated levels of nitrates. Elevated levels of nitrates may be successfully removed from water using treatment processes such as ion exchange, distillation, and reverse osmosis.

The Smyth/Cid Water filtration system is rated by our filter manufacturer, AquaCera, to reduce nitrate contamination by 92%.

It is important to note that with any filtration system, contaminate reduction will slowly diminish over time, which is why it is recommended to change your filter on a regular basis.

Please note: articles on are intended for informational and educational purposes only. Please consult your regional public health official for information regarding the safety of your water supply. In addition, please consult a medical health professional regarding specific concerns regarding nitrates.


  1. Basic Information about Nitrate in Drinking Water, EPA:

  2. Nitrate and Drinking Water from Private Wells, CDC:

  3. Nitrate in Drinking Water, State of Oregon Department of Environmental Quality:

  4. Methemoglobinemia, WHO:

  5. Food sources of nitrates and nitrites: the physiologic context for potential health benefits. The American Journal of Clinical Nutrition:

  6. Nitrates and Nitrites, Answers to Frequently Asked Questions. Ohio Department of Health:

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