01The verdict: is Arco water safe?
Arco's drinking water has significant quality concerns based on EPA testing data. With a grade of A- (85.4/100), the system has issues across multiple categories. A water filter is recommended for all residents. The city's 2 water systems serve approximately 1,139 residents using groundwater (wells).
6 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 3.0 ppb — beneath the 15 ppb federal action level and under the 5 ppb watch threshold.
See the trend ↓3 violations in the last five years
Recent compliance history is the best predictor of future problems — the year-by-year record is below.
See the record ↓Arco's drinking water received a grade of A- (85.4 out of 100), indicating good water quality. The city's 2 water systems serve approximately 1,139 residents using groundwater.
Lead levels were measured at 3.0 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 65 violations on record, including 12 health-based violations. 6 remain unresolved.
Arco ranks #44 out of 139 cities in Idaho for water quality, placing it mid-range in the state. Arco 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, Arco may have fewer resources for advanced treatment technologies and infrastructure upgrades compared to larger utilities.
02What's in Arco's water
Every contaminant flagged in Arco, 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. | 3.0 | 15 | ppb | Inorganic | Safe |
Cities ranked by 90th-percentile lead PF PFAS in Idaho
Cities ranked by compounds detected Cu Copper in Idaho
Cities ranked by 90th-percentile copper
03Arco'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 65 violations on record, including 12 health-based violations. 6 remain unresolved.
6 of the last ten years were clean. The numbered years had EPA violations — red when any were health-based, amber when they were paperwork or missed-testing issues.
▼ Down 0.30 ppb since 2001. Latest reading: 3 ppb (2025) — 20% of the action level. Sampled at higher-risk homes (90th percentile).
04Where Arco's water comes from
Arco'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.
2 systems
2 water systems, operated under local government ownership.
1,139 people
Residents served across Arco'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 1,139 people through 2 water systems.
| System name | PWSID | Population | Source |
|---|---|---|---|
| ARCO CITY OF | ID6120001 | 1,080 | Groundwater |
| BUTTE CITY OF | ID6120002 | 59 | Groundwater |
Water bodies near Arco
These water bodies shape the regional watershed and can indirectly affect groundwater quality.
05Pressure on Arco'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.
Flood & storm history
2 federal disaster declarations on record for Butte County. Flooding and severe storms can overwhelm treatment plants, cause sewage overflows, and push runoff into supplies.
Drought
Butte County is in D3 (extreme 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 Arco compares
Scores for nearby Idaho cities on one line, with the average marked.
dashed line = Idaho average (43/100)
Arco scores 85.4/100 — above the Idaho average of 43/100. It outscores 10 of 10 nearby cities. Full Idaho rankings →
33.6 / 100FMeridian, ID
42.9 / 100FNampa, ID
41.8 / 100DIdaho Falls, ID
46.6 / 100FCaldwell, ID
38.5 / 100FPocatello, ID
42.5 / 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 Arco's water — not generic advice.
A basic carbon filter still helps
Arco'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 →Read your utility's annual report
Every utility must publish a yearly Consumer Confidence Report with its own testing results. It pairs well with the independent data on this page.
How to read a CCR →Watch for Arco alerts
We refresh EPA data monthly and surface new violations, advisories, and boil-water notices for your county on this page.
All water alerts →Frequently asked questions
Is Arco, ID tap water safe to drink?
Arco's water quality earned a grade of A- (85.4/100). The water generally meets EPA standards and is considered safe for consumption. The city ranks #44 out of 139 cities tested in Idaho.
What contaminants are in Arco's water?
Lead was measured at 3.0 ppb (90th percentile). 65 violations are on record.
How is Arco'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 Arco?
Based on current data, basic filtration should suffice for additional peace of mind.
Where does Arco's water come from?
Arco's water is sourced from Groundwater. The city has 2 water systems serving approximately 1,139 residents.
What health violations has Arco's water system had?
Arco has 12 health-based violations on record. The most recent violation was recorded in July 2025. Health-based violations mean the water exceeded EPA maximum contaminant levels (MCLs) for a regulated substance. 6 violations remain unresolved.
Is Arco's groundwater at risk of contamination?
Arco 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 65 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 Arco's water compare to other cities?
Arco ranks #44 out of 139 cities in Idaho (better than 68% of state cities) and #5320 out of 15382 cities nationally (65th percentile). The grade of A- reflects the combined assessment of violation history, lead and copper levels, PFAS contamination, and regulatory compliance.