Water Quality

Nitrate and Nitrite in Well Water: Why Infants Matter Most

Most of the chemical results on a well water report are about taste, staining, or plumbing. Nitrate and nitrite are different: they have health-based limits, set to protect infants. Nitrate is also a particular concern in southeastern Pennsylvania, where farming and development are common. Here’s how to read your results and when to act.

Reading the numbers

Your report lists Nitrate-N and Nitrite-N. The “-N” means the result is reported as the amount of nitrogen, which is the standard way labs report it.

Nitrate-N: limit of 10 mg/L. This is the same as 45 mg/L of nitrate, so don’t be confused if you see that number elsewhere. A result climbing toward 10 is worth watching, and anything above 10 calls for action.
Nitrite-N: limit of 1.0 mg/L. Nitrite is usually below the detection limit in well water. A measurable result is unusual and worth retesting, since it can point to a nearby source of contamination.

Nitrate levels can change with the seasons, rainfall, and nearby land use, so a single test is a snapshot. If your result is elevated, test again in a few months.

Where nitrate comes from

All groundwater contains a little nitrate naturally. Higher levels come from nitrogen that soaks into the ground and reaches the aquifer:

Farm fertilizers and manure spread on fields.
Septic systems, including your own and your neighbors’.
Lawn and garden fertilizer.

Shallow wells, springs, and wells with damaged casings or caps are the most vulnerable. Because the same pathways can carry other contaminants, an elevated nitrate result is also a good reason to consider testing for bacteria and, in farm areas, pesticides.

A related test: MBAS (detergents)

If your test was done for an FHA or VA loan, your report also lists MBAS (methylene blue active substances). It’s a test for detergents and other surfactants, which don’t occur naturally in groundwater. The limit is 0.20 mg/L. A detectable result suggests that household wastewater, usually from a septic system, is reaching the well. Like nitrate, it’s a reason to check the septic system and the well’s construction, and to test for bacteria.

Who is at risk

Infants under 6 months are the main concern. When baby formula is mixed with high-nitrate water, the infant’s body converts nitrate to nitrite, which reduces the blood’s ability to carry oxygen. This condition is called methemoglobinemia, or “blue baby syndrome.” The telltale sign is a bluish tint to the skin, especially around the eyes and mouth. Caught early, it’s readily treated.

Pregnant women should also avoid high-nitrate water, as it has been linked to effects on the developing baby. Nursing mothers don’t pass nitrate to infants through breast milk.

For most healthy adults, nitrate at typical well-water levels isn’t considered a significant health risk. Still, the 10 mg/L limit is a sensible guideline for the whole household.

What to do

If nitrate is above 10 mg/L and there’s an infant or pregnant woman in the home, use bottled water for drinking and for mixing formula right away. Don’t boil the water: boiling doesn’t remove nitrate, and it actually concentrates it as water evaporates.

Next, look for the source:

Check the well. Make sure the casing extends at least a foot above ground, has a sealed cap, and that surface water drains away from it.
Check the septic system. A failing drain field near the well is a common culprit.

If the source is regional, such as nearby farmland, treatment is the practical answer. Nitrate can be removed by:

Reverse osmosis at the kitchen tap, which removes most nitrate from drinking and cooking water. It’s the most common choice for homes.
Anion exchange, a whole-house system similar to a softener, but with resin that swaps nitrate for chloride.
Distillation, effective but slow and energy-intensive.

Retest after installation to confirm the system is working.

The bottom line

Nitrate is one of the few routine well-test results with a health-based limit. If your result is near or above 10 mg/L, and especially if you have a baby on the way or in the home, act on it promptly. Below that, retest periodically, since nitrate levels can change over time.

Chester County Home Inspections provides water quality testing throughout Chester County and the surrounding counties. We collect samples using EPA protocols and deliver them to a PA-DEP certified laboratory. If you have questions about your results, get in touch.