Nitrate in Well Water

Nitrate is a common concern in Delaware's agricultural areas, particularly parts of Kent and Sussex Counties with shallow groundwater.

Private wells

Short answer: Nitrate can come from fertilizer, manure, septic systems, or natural sources, and shallow wells in sandy, agricultural areas are more vulnerable. Test to know your level, and never attribute a result to a specific farm, septic system, or neighbor without evidence.

Why nitrate matters

Nitrate is a common groundwater concern in areas with agricultural land use, septic-system density, and shallow, vulnerable aquifers — conditions found in parts of Kent and Sussex Counties. Elevated nitrate is a particular concern for infants and pregnant women; discuss any elevated result with a health-care provider.

Delaware aquifer context

DNREC's groundwater monitoring describes the Columbia, Frederica, Federalsburg, Cheswold, and Piney Point aquifers in the North Bowers Beach area. The unconfined Columbia aquifer is especially relevant to shallow domestic wells in agricultural Sussex and Kent: a historical DNREC groundwater assessment found higher nitrate vulnerability in the unconfined aquifer, but a county label cannot predict an individual well result. Test your own well and use the result to choose treatment.

University of Delaware's Delaware Geological Survey identifies coastal Delaware groundwater as a primary water source and documents groundwater mixing and pumping conditions in eastern Kent County's Columbia aquifer. That research supports better site-specific questions; it does not establish that every Kent County well has elevated nitrate. For testing logistics, compare the current DPH Environmental Laboratory guidance with a certified laboratory.

Common sources

Agricultural fertilizer application
Manure and livestock operations
Septic system density in an area
Natural soil and geologic sources, in some cases

How to think about a Delaware result

A nitrate result is a measurement from one well at one time. Rainfall, fertilizer timing, pumping, well depth, casing condition, and seasonal recharge can change the concentration. The Columbia aquifer is shallow and important to domestic wells in parts of the state, but an aquifer name does not tell you the result at a specific address. Compare the laboratory result with the current health-based standard, then ask whether confirmation, source investigation, or treatment is needed.

Choosing nitrate treatment

Point-of-use RO or nitrate-specific ion exchange can reduce exposure at a drinking tap when the equipment is certified for nitrate. Whole-house treatment may be appropriate in some homes, but it requires more careful sizing, a drain or regeneration plan, and verification at multiple taps. Activated carbon marketed for taste and odor is not automatically nitrate treatment. Retest after installation and keep the raw and treated results together.

What to do after a result

Compare your result to the current EPA/Delaware health-based reference level with your lab or a qualified professional.
If elevated, consider retesting to confirm and discuss context with your local health department.
Consider treatment (such as reverse osmosis or ion exchange) matched to nitrate specifically, only after testing.
Retest periodically, since nitrate levels can fluctuate seasonally with rainfall and agricultural activity.

Common mistakes

Assuming a single test result won't change over time
Attributing a result to a specific farm or septic system without evidence
Choosing a treatment system not designed for nitrate removal

Retesting and household protection

Retest after a major well repair, flooding, disinfection, treatment change, or unusual rainfall period. If a result is elevated, use the current laboratory and public-health guidance for safe drinking-water decisions, especially when an infant may consume the water. Boiling does not remove nitrate and can concentrate dissolved nitrate as water evaporates.

When treatment is installed, collect both an untreated sample and a treated sample under the laboratory's instructions. Test the drinking tap that the household actually uses. A treatment claim should identify nitrate specifically; general sediment, taste, or odor filters should not be treated as nitrate protection.

Questions for the laboratory

Ask whether the result is reported as nitrate or nitrate-nitrogen, which units apply, what reporting limit was used, and whether the sample was preserved correctly. Ask when a confirmation sample should be collected and whether the lab recommends a broader panel based on the property. These details prevent a unit-conversion or sampling issue from leading to the wrong treatment decision.

Keep the laboratory report with the well record and note whether the sample was collected before or after treatment. If several homes in an area report concerns, coordinate with the county health unit or DNREC rather than trying to infer a source from one property’s result.

Use the same laboratory and units when comparing repeat samples whenever possible.

Official sources

U.S. EPA nitrate drinking-water guidance
DNREC groundwater monitoring and aquifer information
Delaware Public Health Laboratory and certified laboratories
Delaware Geological Survey RI86: Kent County groundwater and salinization

Does nitrate fluctuate seasonally?

Yes, nitrate levels can change with rainfall, irrigation, and agricultural activity nearby. A single sample reflects conditions at the time of collection, not a permanent baseline.

This page provides general educational information and is not medical or laboratory advice.

Last reviewed: 2026-07-11. Report a correction.