Nitrates and Nitrites in Drinking Water


What are the health effects of drinking water that contains nitrates and nitrites?

There are two health concerns when drinking water with high levels of nitrates or nitrites. The first health concern is with infants being at risk for “blue baby syndrome”, also called methemoglobinemia:

The second health concern with nitrates and nitrites is the formation of chemicals called nitrosamines in the digestive tract. Nitrosamines are being studied for long term links to cancer. No standards have been set for this yet.

Can "blue baby syndrome" affect children and adults?

There is no danger of blue baby syndrome for adults or older children or to breastfed infants. Research continues on the effects of nitrates and nitrites during pregnancy. The safest choice for pregnant women is to drink water that does not have high levels of nitrates or nitrites, so well water should be tested.

How else could you be exposed to nitrates and nitrites?

Exposure to nitrates usually comes from food that we eat. Many vegetables and cured meats contain nitrates and to a lesser extent nitrites.

Nitrates and nitrites in water are not a health concern when showering or bathing.

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Where do nitrates and nitrites come from?

Nitrogen can take different forms in nature and is important for life in both plants and animals. The most common form of nitrogen found in well water is nitrate.

Wells with high levels of nitrates are more likely to be privately owned and/or shallow, and affected by human activity. If human or animal waste contaminates a well, nitrites will be detected first but will quickly convert to nitrates. Therefore, most well water tests are done for nitrates.

Possible sources of nitrates and nitrites:

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How can drinking water be tested for nitrates?

The Vermont Department of Health offers a screening test "Kit C" for wells that includes nitrate. When you receive test results they will be compared with maximum levels.

Order a test kit by calling the Public Health Laboratory at 1-800-660-9997.

What is the maximum concentration for nitrates and nitrites in drinking water?

The U.S. Environmental Protection Agency (EPA) sets Maximum Contaminant Levels (MCLs) for nitrogen in public drinking water systems. Vermont has adopted these standards. The MCL for nitrates is 10 milligrams per liter (NO3 –N mg/l). The MCL for nitrites is one milligram per liter (NO2 –N mg/l).

What are recommended steps to take if tests find higher than acceptable levels of nitrates?

Well water with a nitrate level equal to or greater than 10 milligrams per liter (mg/l) should not be used for drinking or food preparation. When the level of nitrate exceeds five mg/l, try to identify the source of nitrate and make a plan to reduce or remove it if possible. Use an alternative known safe source of water or bottled water until nitrate levels can be reduced to an acceptable level.

Treatment of the water source may be needed if efforts to remove/reduce the source of the nitrates are not successful in lowering levels. Boiling water will not reduce nitrate levels.

Other alternatives include:

The location of a new well should be investigated thoroughly by a qualified professional, such as an engineer or hydrogeologist, because it is possible that nitrates have entered the groundwater aquifer under a wide area.

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How is drinking water treated to remove nitrates?

Treatment methods such as anion exchange and reverse osmosis can remove nitrates from drinking water.

Anion exchange uses equipment and technology similar to a water softener. It treats all the water for the home. The nitrates are removed from the water as they are exchanged for (harmless) chlorides. The chlorides are supplied from a salt tank which must be re-filled on a schedule.

Reverse osmosis uses a membrane through which water (but not nitrates) can travel. The system is typically installed beneath the kitchen sink with a small tank holding the nitrate-free water. Water used for drinking and food preparation comes from this tank under the sink. If the well water is hard or contains too much iron, a softener or iron removal system must be installed before using the reverse osmosis system.

Consult a water treatment specialist. You can locate one by looking in the yellow pages. After installation of either treatment listed above, it is strongly recommended that proper maintenance and periodic testing of nitrates be planned to ensure that the system is working effectively.

Caution: Nitrate treatments are not effective against bacterial contamination. If nitrate levels are thought to be linked to manure or household wastewater, test the drinking water also for bacterial contamination.

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