01The verdict: is North Sioux City water safe?
North Sioux City's tap water meets most EPA standards but has areas that warrant attention. With a grade of A (91/100), some contaminant levels or compliance issues suggest that residents may benefit from additional filtration. The city's 1 water system serves approximately 3,042 residents using groundwater (wells).
2 unresolved violations on record
EPA records show open compliance items for this system. Most are administrative, but unresolved items are worth watching.
See what was cited ↓Lead is well under the limit
90th-percentile lead is 4.0 ppb — beneath the 15 ppb federal action level and under the 5 ppb watch threshold.
See the trend ↓A flood-prone service area
10 federal disaster declarations on record. After severe weather, watch for boil-water advisories.
See the risk factors ↓North Sioux City's drinking water received a grade of A (91 out of 100), indicating excellent water quality. The city's 1 water system serves approximately 3,042 residents using groundwater.
Lead levels were measured at 4.0 ppb (90th percentile), well within EPA limits. This system has not yet been tested for PFAS under the EPA UCMR 5 program. The system has 35 violations on record, including 0 health-based violations. 2 remain unresolved.
North Sioux City ranks #35 out of 137 cities in South Dakota for water quality, placing it above average in the state. North Sioux City relies on groundwater, which is generally less vulnerable to surface contamination but can be affected by naturally occurring minerals like arsenic and nitrate, as well as agricultural and industrial runoff. As a small community water system, North Sioux City may have fewer resources for advanced treatment technologies and infrastructure upgrades compared to larger utilities.
02What's in North Sioux City's water
Every contaminant flagged in North Sioux City, on one shared scale: distance to its own legal limit. The red line is the limit — anything past it is out of compliance, and the closer a bar gets, the less headroom the system has.
Full contaminants report
| Contaminant | Detected Level | EPA Limit | Unit | Category | Status |
|---|---|---|---|---|---|
| Lead (90th percentile) LeadHeavy Metal A toxic heavy metal that can leach into drinking water from older pipes, solder, and fixtures. No amount of lead in water is considered safe. Health EffectsBrain and nervous system damage in children, kidney damage, high blood pressure, and reproductive problems in adults. EPA Limit15 ppb action level Common SourcesCorrosion of lead pipes, lead solder, brass faucets, and household plumbing. | 4.0 | 15 | ppb | Inorganic | Safe |
Cities ranked by 90th-percentile lead PF PFAS in South Dakota
Cities ranked by compounds detected Cu Copper in South Dakota
Cities ranked by 90th-percentile copper
03North Sioux City's ten-year track record
Each box is one year. A green check means no EPA violations; a numbered badge counts that year's violations — red if any were health-based, amber if they were monitoring or paperwork issues. The system has 35 violations on record, including 0 health-based violations. 2 remain unresolved.
All ten of the last ten years were clean — no EPA violations recorded for North Sioux City.
▲ Up 1 ppb since 1993. Latest reading: 4 ppb (2023) — 27% of the action level. Sampled at higher-risk homes (90th percentile).
04Where North Sioux City's water comes from
North Sioux City's drinking water is drawn from underground aquifers through wells.
Groundwater
Underground aquifers reached by wells — naturally filtered, but can carry minerals like arsenic and nitrate.
Local treatment
Groundwater generally needs less treatment — typically disinfection and, where needed, mineral removal.
1 system
1 water system, operated under local government ownership.
3,042 people
Residents served across North Sioux City's service area.
Groundwater is naturally filtered through rock and soil layers, generally requiring less treatment than surface water. However, it can contain naturally occurring contaminants like arsenic, radon, and minerals. Agricultural activity, septic systems, and industrial operations near well fields can introduce nitrates, pesticides, and volatile organic compounds. The system is operated by local government ownership and serves approximately 3,042 people through 1 water system.
| System name | PWSID | Population | Source |
|---|---|---|---|
| NORTH SIOUX CITY | SD4600226 | 3,042 | Groundwater |
Water bodies near North Sioux City
These water bodies shape the regional watershed and can indirectly affect groundwater quality.
05Pressure on North Sioux City's watershed
Outside forces that shape what reaches the treatment plant. None of these is a verdict on the tap by itself — but each adds pressure worth knowing about.
Industrial discharge
5 facilities within 10 miles reported 193 lb released to surface water in the latest EPA Toxics Release Inventory. Proximity doesn't equal tap contamination — treatment and hydrology decide — but it's pressure on the watershed.
Flood & storm history
10 federal disaster declarations on record for Union County. Flooding and severe storms can overwhelm treatment plants, cause sewage overflows, and push runoff into supplies.
Drought
Union County is in D2 (severe drought) per the U.S. Drought Monitor (week of Jul 2026). Drought can raise disinfection-byproduct levels and taste/odor issues as utilities draw from lower reservoirs.
06How North Sioux City compares
Scores for nearby South Dakota cities on one line, with the average marked.
dashed line = South Dakota average (66/100)
North Sioux City scores 91/100 — above the South Dakota average of 66/100. It outscores 8 of 10 nearby cities. Full South Dakota rankings →
58.2 / 100FRapid City, SD
38.7 / 100FAberdeen, SD
41.8 / 100AWatertown, SD
91 / 100FPine Ridge, SD
43.2 / 100DBrookings, SD
46.2 / 100
Compare all cities in the county — grades, violations, and contaminant data side by side.→
07What to do at home
Steps matched to what testing actually found in North Sioux City's water — not generic advice.
A basic carbon filter still helps
North Sioux City's water meets federal standards, but a simple carbon filter improves taste and adds a margin of safety against short-term issues.
Compare tested filters →Flush taps & check your service line
Lead leaches from pipes as water sits. Run cold water 30 seconds before drinking (especially mornings), and ask the utility whether your address still has a lead service line.
Lead risks explained →Watch for North Sioux City alerts
This area has a history of flood declarations — after severe weather, watch for boil-water advisories from the utility, and check the live alerts on this page.
All water alerts →Frequently asked questions
Is North Sioux City, SD tap water safe to drink?
North Sioux City's water quality earned a grade of A (91/100). The water generally meets EPA standards and is considered safe for consumption. The city ranks #35 out of 137 cities tested in South Dakota.
What contaminants are in North Sioux City's water?
Lead was measured at 4.0 ppb (90th percentile). 35 violations are on record.
How is North Sioux City's water quality grade calculated?
The grade is based on four factors: violation history (40%), lead and copper levels (25%), PFAS contamination (25%), and regulatory compliance (10%). The score is also adjusted based on how complete the available data is. See our methodology page for full details.
Do I need a water filter in North Sioux City?
Based on current data, basic filtration should suffice for additional peace of mind.
Where does North Sioux City's water come from?
North Sioux City's water is sourced from Groundwater. The city has 1 water system serving approximately 3,042 residents.
Is North Sioux City's groundwater at risk of contamination?
North Sioux City uses groundwater, which can be affected by naturally occurring contaminants like arsenic, radon, and nitrate, as well as agricultural runoff and industrial activity. The system has 35 violations on record that may relate to groundwater quality. Groundwater systems are generally less susceptible to surface contamination but should be monitored for emerging contaminants like PFAS.
How does North Sioux City's water compare to other cities?
North Sioux City ranks #35 out of 137 cities in South Dakota (better than 74% of state cities) and #1925 out of 15382 cities nationally (88th percentile). The grade of A reflects the combined assessment of violation history, lead and copper levels, PFAS contamination, and regulatory compliance.
Does North Sioux City's small water system affect quality?
North Sioux City's system serves approximately 3,042 residents. Small community water systems (under 3,300 people) may have fewer financial resources for infrastructure upgrades and advanced treatment technologies. However, they are held to the same EPA drinking water standards as larger systems. This system has 35 violations on record.