South Dakota
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South Dakota water profile

Nitrate in South Dakota community water systems

South Dakota's reporting systems run low: of the 183 with a current result — 40% of the state's 463 — almost none reach 5 mg/L, and the mid-band systems that do show up scatter across the glaciated east. See the pattern and what each reporting system measured in the three years from August 9, 2023 to August 9, 2026.

Browse all 183 South Dakota systems →

Search by the utility or system name shown on a water bill. Example: City of Sioux Falls. Private wells are not in this inventory.

40%
of the state’s 463 active community water systems have a current result here
183
systems with a current nitrate result
530,501
people served by those reporting systems
0.5%
of reporting systems at or above 5 mg/L
How to read these numbers Each system is placed into a band by its most recent reported result within a rolling three-year window. The bands describe how strongly human activity, read from nitrate, has marked a water source; they are not a safety verdict. Figures describe system reporting, not nitrate measured at an individual tap.

How South Dakota's systems fall across the five bands

Most systems report below 3 mg/L

Natural background
0.00–0.99 mg/L as N
123 systems · 464,984 served
Human impact likely
1.00–2.99 mg/L as N
28 systems · 29,010 served
Human impact clear
3.00–4.99 mg/L as N
31 systems · 35,809 served
Health-study range
5.00–9.99 mg/L as N
1 system · 698 served
Above the federal limit
10.00 mg/L and above
0 systems · 0 served

Each system appears in one band only, placed by its most recent reported result in the current three-year window. Counts sit beside people served so a small number of larger systems cannot hide behind a row of tiny ones. The one system reporting 5 mg/L or more did not stay there across its whole three-year range — it reached 5 only on a high sample and otherwise ran lower.

Most recent reading Oct 2025; the typical system was last tested around Oct 2025. 150 systems sampled their own water; 33 systems carry a supplier’s result.

The named systems

Every reading here belongs to a utility with a name

Highest recent readings
SystemMost recent resultBandBased onPeople served
Castlewood7.10 mg/La high point — runs lowerHealth-study rangeCCR summary, unverified698
Rimrock Heights Homeowners Associati4.91 mg/LHuman impact clearCCR summary, unverified35
Reynolds Court4.85 mg/LHuman impact clearCCR summary, unverified28
Bryant4.80 mg/LHuman impact clearCCR summary, unverified471
Estelline4.80 mg/LHuman impact clearCCR summary, unverified749
Sioux Rural Water System4.80 mg/LHuman impact clearCCR summary, unverified4,280
Siphon Hill Water Association4.46 mg/LHuman impact clearCCR summary, unverified68
Bonesteel4.10 mg/LHuman impact clearinherited from supplier275
Largest systems
SystemMost recent resultBandBased onPeople served
Sioux Falls0.45 mg/LNatural backgroundCCR summary, unverified216,462
Rapid City0.76 mg/LNatural backgroundCCR summary, unverified72,009
Brookings Municipal Utilities0.05 mg/LNatural backgroundCCR summary, unverified23,377
Minnehaha Community Water Corp0.50 mg/LNatural backgroundCCR summary, unverified13,435
Spearfish0.60 mg/LNatural backgroundCCR summary, unverified12,193

Each result shows its date and what it rests on, so a lone sample is never taken for a settled measurement. A single high sample is not a complete account of what a household drinks.

Where higher nitrate concentrates

A light scatter across the glaciated east

Human impact is clear on drinking water served in twelve of South Dakota’s 66 counties. Each is shaded by how many of its systems reported 3.00 mg/L as N or above. Shading counts systems, not severity — a county with many small utilities can outrank one holding a single larger system that reads higher. The table beside the map splits the two bands so that difference stays visible.

SD counties shaded by number of community water systems reporting nitrate at or above 3.00 mg/L as NCounties are shaded by how many community water systems reported nitrate at or above 3.00 mg/L as N in the three years from August 9, 2023 to August 9, 2026. The same counts appear in the table below this map.Lawrence County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveLake County — 2 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveClark County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveGregory County — 4 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveCodington County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveKingsbury County — 2 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or abovePennington County — 6 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveTripp County — 2 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveMoody County — 4 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveBrookings County — 4 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveHamlin County — 2 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveDeuel County — 2 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or above
none1–23–56–1112–2526+Number of drinking water systems reporting ≥3.00 mg/L NO₃–N per county as of August 9, 2026

Hamlin leads this layer with 1 reporting system. A light scatter across the glaciated east.

Counties with the most systems at or above 3 mg/L as N
County3–4.99≥5Total ≥3
Pennington606
Brookings404
Gregory404
Moody404
Hamlin213

Counts use each system's most recent reported result in the current three-year window. A system appears in only one of the two bands.

Find a specific South Dakota system

What the statewide pattern says

Glacial till keeps a lid on it — mostly

South Dakota's signal is thin because its dominant aquifer is heterogeneous glacial drift — median nitrate in its private wells is among the lowest measured nationally, with pockets of high readings in shallow oxidizing settings.

East of the Missouri River, South Dakota drinks from the glacial aquifer system — buried outwash and till left by the ice sheets. Nationally, USGS found that system runs low: median nitrate of just 0.11 mg/L in private wells, background under 1 mg/L, and fewer than 5 percent of private wells above the federal limit — though that small group included some of the highest nitrate ever measured by the national program, up to 77 mg/L (USGS Scientific Investigations Report 2010-5100).

The glacial drift’s heterogeneity is the control. Thick, fine-grained, reducing till strips nitrate; shallow, oxidizing sand-and-gravel windows let it through. Mapping the whole glacial system, USGS estimated high nitrate in about 4 percent of its area, concentrated where groundwater stays oxidizing and nitrogen sources sit close (Erickson and others, 2019). South Dakota’s mid-band counties — Pennington, Brookings, Gregory, Moody — mark such windows rather than any regional driver.

West of the river the state shifts to bedrock aquifers — the Minnelusa and Madison in the Black Hills, the Dakota and Niobrara elsewhere — whose nitrate typically runs low where wells are deep and well-sealed; the state literature treats high readings there as local surface leakage rather than a regional pattern.

The supported source reading is local agricultural nitrogen entering shallow oxidizing windows in the glacial drift — not a certified source at any individual system, and in South Dakota a genuinely small pattern (Nolan and Hitt, 2006).

The general science — how nitrate moves, why some ground is vulnerable, and why the legacy lingers — is laid out with its sources on Where nitrate comes from.

Questions this page answers

What the South Dakota pattern does—and does not—say

Where does nitrate concentrate in South Dakota community water systems?

Hamlin leads this layer with 1 reporting system. A light scatter across the glaciated east.

Why is South Dakota's nitrate signal so thin?

Its dominant eastern aquifer is heterogeneous glacial drift: thick, fine-grained, reducing till strips nitrate before it reaches most wells. USGS measured a 0.11 mg/L median in the glacial system's private wells — among the lowest in the national program. High readings survive only in shallow, oxidizing sand-and-gravel windows.

If the state runs low, is testing still worth it?

Yes, for shallow wells. The glacial system's few high wells included some of the highest nitrate the national USGS program ever recorded (up to 77 mg/L), and those wells sit in exactly the shallow, unregulated setting that public-system data cannot see.

Does a high public-system result mean a nearby private well is high?

No. It is a local sentinel, not a well-specific result. It shows that nitrogen and a transport pathway have reached groundwater in the area; a certified-lab test is still the only way to know a specific private well.

Sources and provenance

What this page rests on

  1. NitrateSmart inventory: 183 South Dakota community water systems with a current nitrate result in the three years from August 9, 2023 to August 9, 2026. Figures count people served by reporting systems, not measured tap exposure.
  2. Nolan BT, Hitt KJ (2006). Vulnerability of Shallow Groundwater and Drinking-Water Wells to Nitrate in the United States. Environmental Science & Technology 40(24):7834–7840.
  3. Dubrovsky NM, and others (2010). Nutrients in the Nation's Streams and Groundwater, 1992–2004. USGS Circular 1350.
  4. USGS (2010). Relations That Affect the Probability and Prediction of Nitrate Contamination in the Glacial Aquifer System in the United States. Scientific Investigations Report 2010-5100 — private-well median 0.11 mg/L; <5% above the MCL; extremes to 77 mg/L.
  5. Erickson ML, and others (2019). Drinking water quality in the glacial aquifer system, northern USA. Science of the Total Environment — high nitrate in ~4% of the glacial system area; rare in fine-grained reducing terranes.