The limit, and the two scales it can be written on
The federal maximum contaminant level for nitrate is 10 mg/L, and the survey that samples Kansas groundwater states it that way in its 2025 annual report[1]. The Kansas Geological Survey circular of June 1999 records who set it, the Environmental Protection Agency and KDHE, and gives the unit as nitrate as nitrogen[3]. The K-State Research and Extension sheet of April 1999 gives the same figure the other way round, 10 parts per million of nitrate-nitrogen[4].
That distinction is not pedantry, because two scales are in circulation and they differ by a factor of four and a half. The 1999 sheet sets them out: laboratories certified for drinking water tests report nitrate-nitrogen, and some laboratories doing feed analysis report nitrate. Dividing a nitrate figure by 4.5 converts it, so 45 mg/L of nitrate is the same water as 10 mg/L of nitrate-nitrogen[4]. A result with no scale attached to it is not a result.
Natural background is well below the limit. The 1999 circular put naturally occurring nitrate-nitrogen at nearly always less than 3 mg/L, and read anything above that as a sign that nitrate from non-natural sources such as human or animal waste or fertilizers had entered the groundwater[3]. The extension sheet of the same year put the threshold at 3 to 4 parts per million, and noted that nitrate is tasteless, odorless and colorless[4].
Where it concentrates, and why there
The survey reported in 1999 that groundwater was the major source of drinking water for 70 percent of Kansas residents, and that in rural areas 85 percent of the population relied on it. It called nitrate the most common inorganic contaminant in it[3].
The same 1999 circular named the physical conditions that concentrate it, and they are common in this state: relatively permeable sandy soils, a shallow water table, shallow wells and irrigated farming. It named south-central Kansas as the clearest example. It also found that water from wells built before 1975 carried higher nitrate-nitrogen than water from newer ones, which it linked to construction: older wells commonly had the annular space filled with gravel pack close to the land surface. KDHE adopted regulations on water-well construction and abandonment in 1975[3].
Nitrogen fertilizer sales in Kansas rose steeply from the mid-1940s, and the Kansas Department of Agriculture recorded over 700,000 tons sold in 1997. Beef cattle waste is the largest animal source. Point sources include concentrated livestock confinement, leaking septic or sewer systems, and unplugged abandoned wells and boreholes, which give surface contamination a direct route down[3].
The current sampling program describes the geography the same way. Its 2025 map note reads elevated nitrate as widespread across Kansas, lower in the eastern and southeastern parts of the state where crop-based agriculture is less common, and higher through the center of the state where it is prevalent and the groundwater is relatively shallow[1].
The program that stopped for 23 years
The United States Geological Survey began sampling Kansas groundwater quality in 1985, taking roughly 180 to 240 wells a year through 1991 and 1,332 samples in all. KDHE took the program over in 1992, sampling between 80 and 140 wells a year, 1,070 samples from 301 wells, with none collected in 1998. Funding was eliminated after the 2001 sampling year. KDHE determined in 2023 that it should be reinstated and granted the work to the Kansas Geological Survey in 2024[5].
That gap is why nearly every nitrate percentage in circulation about Kansas is a 1990s figure. The often-quoted finding that about 30 percent of domestic wells in Kansas exceed the limit is attributed by the survey to four studies published between 1988 and 1996[3]. The extension sheet reported 24 percent of private wells and 28 percent of farmstead wells above the standard from surveys it describes only as recent, in a publication dated April 1999[4]. Neither is a current measurement and neither was ever meant to be read as one 27 years later.
The restarted program sampled 151 wells in 2024 and 166 in 2025, and it moved deliberately toward domestic wells in the second year: 104 of the 2025 wells were domestic, against 38 the year before. Of the 143 production wells sampled in 2025, 12 samples exceeded the nitrate limit, which the survey reports as 8.39 percent. The 23 monitoring wells are excluded from that denominator by the survey itself, on the stated ground that they were chosen where elevated analytes were suspected and so do not represent aquifer conditions where a production well would be placed[1].
In 2025 the program went back to the ground around wells that had failed the year before. Of the 151 wells sampled in 2024, 12 were above 10 mg/L. Letters went to 41 well owners within a mile of those wells offering a free sample; six responded and four wells were sampled. Two of the four came back above the limit, which the survey reads as likely indicating a regional issue. At Downs the well that prompted the study read 14.95 mg/L and the neighboring well 12.72. At Wakefield the two readings were 60.28 and 17.25. At Topeka the first read 10.60 and the two neighbors 3.90 and 4.22[1].
Public systems that went over the limit
KDHE holds primacy for the Safe Drinking Water Act in Kansas, so every compliance determination the department makes about a public water system is reported into the federal Safe Drinking Water Information System. Counting the distinct Kansas systems in that record with a nitrate maximum contaminant level violation whose compliance period began in the year gives the table below. It is a count made over the federal extract as it stood on September 2, 2026, not a figure the agency printed, and a system appears once for each quarterly compliance period, which is why the record count runs two to three times the system count[2].
In that same extract the 19 systems recorded for 2025 were 17 community water systems and two transient non-community systems. They serve populations ranging from 25 people to 6,573, and the recorded concentrations in those violations run from 11 mg/L to 20 mg/L. All but one of the 19 served fewer than 2,100 people[2].
A system over the limit is not left there. Twenty-seven years ago the extension sheet reported about 40 Kansas public water supplies that had obtained an alternative water source, drilled new wells, installed treatment equipment or were working on plans to meet the nitrate standard[4].
| Year | Systems | Violation records |
|---|---|---|
| 2021 | 18 | 42 |
| 2022 | 14 | 41 |
| 2023 | 22 | 57 |
| 2024 | 23 | 59 |
| 2025 | 19 | 51 |
How a private well gets tested here
None of the above applies to a private well. The 1999 circular found most private domestic supplies in Kansas neither tested nor treated on a routine basis[3], and the 2025 sampling report says domestic wells are sampled much less frequently than public supply wells, if at all[1]. There is no schedule, no reporting duty and no database.
The route KDHE describes starts with the county. The Kansas Health and Environmental Laboratories stopped testing private well samples for coliform, on the department's stated reasoning that assessing a private supply requires an assessment of the well's location and construction and a site assessment for contaminants, and that a single sample is not indicative of the overall safety of the water. The department directs a well owner to a local health department, a local sanitarian or a KDHE district office, and says an owner who wants a routine test should be referred to a private laboratory certified by that state laboratory[6]. The department's Private Well Resource Map is where those contacts are listed together. It carries county sanitarian details, including whether a county provides sampling kits or a sampling service, and marks certified laboratories that test private wells. Those laboratories were selected on two analytes, coliform bacteria and nitrate, which the department says to test for first[7].
The county extension office is a second route. Both of the standing Kansas documents on nitrate come out of it: the fact sheet is a K-State Research and Extension publication[4], and the survey's own circular directs inquiries to the Cooperative Extension Service at Kansas State University, to county health departments and to local Natural Resource Conservation Service district offices[3]. The restarted sampling program is a third: 109 people asked to have a well sampled through its website in 2025, against 59 in 2024, and it publishes results to a public online mapper[1].
What a test is, and who performs it, is the whole of what belongs on a page like this one. The sampling itself is a certified laboratory's instruction to give or a sanitarian's, and both of the 1999 documents give it at length. A reader who came here for one figure and wants the rest of what Kansas measures about itself can start at the front page.