Tap Water Quality Report
Tap water quality in TWIN FALLS, Idaho
Tap water in TWIN FALLS, Idaho receives a grade of F (57/100) from TapWaterSafety.org. It's served by TWIN FALLS CITY OF. The most significant water quality concerns are: Arsenic significantly above health guideline; Haloacetic acids (HAA9) significantly above health guideline; Total trihalomethanes (TTHMs) significantly above health guideline. Data sources: EPA SDWIS, EPA ECHO, EWG Tap Water Database.
What's in TWIN FALLS's tap water
Top water quality concerns identified by the EPA and Environmental Working Group across the utility serving TWIN FALLS.
Arsenic significantly above health guideline
Moderate concernArsenic detected at 5.26 ppb, 1315x above the EWG health guideline of 0.004 ppb.
Haloacetic acids (HAA9) significantly above health guideline
Moderate concernHaloacetic acids (HAA9) detected at 15.4 ppb, 256x above the EWG health guideline of 0.06 ppb.
Total trihalomethanes (TTHMs) significantly above health guideline
Moderate concernTotal trihalomethanes (TTHMs) detected at 26.6 ppb, 177x above the EWG health guideline of 0.15 ppb.
EPA compliance record
Official U.S. EPA records for TWIN FALLS CITY OF (system ID ID5420058) for the last 3 years. Checked 2026-10-07.
| Rule | Type | Since | Status |
|---|---|---|---|
| Revised Total Coliform Rule | Missed testing | 02/01/2026 | Open |
| Ground Water Rule | Missed testing or reporting | 02/17/2015 | Open |
| Nitrate Rule | Missed testing or reporting | 01/01/2023 | Open |
| Stage 1 Disinfectants and Disinfection Byproducts Rule | Missed testing or reporting | 02/01/2026 | Open |
| Lead and Copper Rule | Missed testing or reporting | 07/01/2022 | Open |
Source: U.S. EPA Enforcement and Compliance History Online (ECHO), from the Safe Drinking Water Information System. See EPA's full report.
Recommended filters for TWIN FALLS
Filters matched to the specific contaminants in TWIN FALLS's water supply.
Reverse osmosis certified for arsenic (NSF/ANSI 58)
$429-$599Reverse osmosis certified under NSF/ANSI 58 for arsenic is the most reliable home option.
Carbon filter certified for VOCs (NSF/ANSI 53)
$180-$599Activated carbon is effective for disinfection byproducts. Look for NSF/ANSI 53 VOC reduction.
Disclosure: TapWaterSafety earns a commission from purchases made through these links. This does not influence our scoring methodology or filter selection.
All contaminants detected in TWIN FALLS's tap water
Every contaminant identified, compared side-by-side against US EPA legal limits, the EU Drinking Water Directive (2020/2184), WHO Guidelines, and California's Public Health Goal. Why we show multiple standards →
| Contaminant | Detected | EWG US health-based |
EPA US legal |
EU DWD Europe |
WHO global |
CA PHG strictest US |
Tested sample year |
Status |
|---|---|---|---|---|---|---|---|---|
| Arsenic Heavy metal |
5.26 ppb | 0.004 | 10.0 | 10 | 10 | 0.004 | — | 1315× over |
| Haloacetic acids (HAA9) Disinfection byproduct |
15.4 ppb | 0.06 | — | — | — | — | — | 256× over |
| Total trihalomethanes (TTHMs) Disinfection byproduct |
26.6 ppb | 0.15 | 80.0 | 100 | — | — | — | 177× over |
| Dibromoacetic acid Disinfection byproduct |
4.05 ppb | 0.03 | — | — | — | — | — | 135× over |
| Dibromochloromethane Disinfection byproduct |
10.5 ppb | 0.1 | — | — | — | — | — | 105× over |
| Bromodichloromethane Disinfection byproduct |
4.85 ppb | 0.06 | — | — | — | — | — | 81× over |
| Chromium (hexavalent) Heavy metal |
0.954 ppb | 0.02 | — | — | — | — | — | 48× over |
| Haloacetic acids (HAA5) Disinfection byproduct |
4.53 ppb | 0.1 | 60.0 | 60 | — | — | — | 45× over |
| Bromoform Disinfection byproduct |
9.17 ppb | 0.5 | — | — | — | — | — | 18× over |
| Nitrate Inorganic |
2.31 ppm | 0.14 | 10.0 | 11.3 | 11.3 | 10 | — | 16× over |
| Nitrate and nitrite Inorganic |
2.28 ppm | 0.14 | 10.0 | 11.3 | 11.3 | 10 | — | 16× over |
| Radium, combined (-226 and -228) Radiological |
0.7 pCi/L | 0.05 | 5.0 | — | — | — | — | 14× over |
| Uranium Radiological |
3.15 pCi/L | 0.43 | 20.0 | 30 | 30 | 0.43 | — | 7.3× over |
| Chloroform Disinfection byproduct |
1.29 ppb | 0.4 | — | — | — | — | — | 3.2× over |
| Vanadium Other |
21.8 ppb | 21.0 | — | — | — | — | — | 1.0× over |
| Molybdenum Other |
2.73 ppb | 40.0 | — | — | — | — | — | Below guideline |
| Chlorate Disinfection byproduct |
9.38 ppb | 210.0 | — | — | — | — | — | Below guideline |
| Strontium Radiological |
0.428 ppb | 1500.0 | — | — | — | — | — | Below guideline |
| Chlorodifluoromethane Other |
0.0435 ppb | — | — | — | — | — | — | Below guideline |
All values in the unit of the detected level. Red cells indicate the detected level exceeds that standard. Some contaminants have limits in some jurisdictions but not others (shown as —). The "Tested" column shows the year each contaminant sample was collected.
Sources: US EPA, EU Drinking Water Directive 2020/2184, WHO Guidelines, California OEHHA PHGs, EWG Tap Water Database.
Treatment plant contact info
For service issues, water quality concerns, or to request a Consumer Confidence Report from TWIN FALLS CITY OF.