01The verdict: is Thermal water safe?
Thermal's drinking water has significant quality concerns based on EPA testing data. With a grade of D (48/100), the system has issues across multiple categories. A water filter is recommended for all residents. The city's 17 water systems serve approximately 3,056 residents using groundwater (wells).
171 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 5.0 ppb — beneath the 15 ppb federal action level and under the 5 ppb watch threshold.
See the trend ↓370 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 ↓Thermal's drinking water received a grade of D (48 out of 100), indicating poor water quality. The city's 17 water systems serve approximately 3,056 residents using groundwater.
Lead levels were measured at 5.0 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 1172 violations on record, including 127 health-based violations. 171 remain unresolved.
Thermal ranks #619 out of 690 cities in California for water quality, placing it among the lowest-rated in the state. Thermal 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, Thermal may have fewer resources for advanced treatment technologies and infrastructure upgrades compared to larger utilities. The system has seen 370 violations in the past five years, suggesting a pattern of compliance challenges that residents should monitor closely.
02What's in Thermal's water
Every contaminant flagged in Thermal, 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. | 5.0 | 15 | ppb | Inorganic | Safe |
Cities ranked by 90th-percentile lead PF PFAS in California
Cities ranked by compounds detected Cu Copper in California
Cities ranked by 90th-percentile copper
03Thermal'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 1172 violations on record, including 127 health-based violations. 171 remain unresolved.
1 of the last ten years was clean. The numbered years had EPA violations — red when any were health-based, amber when they were paperwork or missed-testing issues.
▼ Down 0 ppb since 2002. Latest reading: 5 ppb (2025) — 33% of the action level. Sampled at higher-risk homes (90th percentile).
04Where Thermal's water comes from
Thermal'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.
17 systems
17 water systems, operated under private ownership.
3,056 people
Residents served across Thermal'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 private ownership and serves approximately 3,056 people through 17 water systems.
| System name | PWSID | Population | Source |
|---|---|---|---|
| Oasis Mobile Home Park | 090605129 | 1,350 | Groundwater |
| Torres-Martinez Clinic | 090605130 | 379 | Purchased Groundwater |
| AMEZCUA - GARCIA WATER | CA3301990 | 316 | Groundwater |
| DD Mobile Home Park | 090605160 | 300 | Groundwater |
| Torres-Martinez Avenue 64 | 090605116 | 180 | Groundwater |
| Montano Ranch | 090600038 | 72 | Groundwater |
| Toledo MHP | 090600021 | 68 | Groundwater |
| Ramon Zaragoza Water | 090600036 | 51 | Groundwater |
| Gamez MHP | 090600029 | 48 | Groundwater |
| El Mesquite MHP | 090600034 | 48 | Groundwater |
| Castro Ranch | 090600027 | 44 | Groundwater |
| Gonzalez MHP | 090600022 | 41 | Groundwater |
| Ranchos Los Ferro MHP | 090600032 | 41 | Groundwater |
| Sandoval MHP | 090600026 | 38 | Groundwater |
| Arellano MHP | 090600023 | 30 | Groundwater |
| Barajas MHP | 090600031 | 25 | Groundwater |
| Garcia MHP | 090600037 | 25 | Purchased Groundwater |
Water bodies near Thermal
These water bodies shape the regional watershed and can indirectly affect groundwater quality.
05Pressure on Thermal'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
2 facilities within 10 miles reported 0 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 Riverside County. Flooding and severe storms can overwhelm treatment plants, cause sewage overflows, and push runoff into supplies.
Drought
Riverside County is in D1 (moderate 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 Thermal compares
Scores for nearby California cities on one line, with the average marked.
dashed line = California average (57/100)
Thermal scores 48/100 — below the California average of 57/100. It outscores 5 of 10 nearby cities. Full California rankings →
42.8 / 100FSan Jose, CA
28 / 100BOakland, CA
77.9 / 100FSan Diego, CA
39.7 / 100FSacramento, CA
31.2 / 100ABurlingame, CA
89.2 / 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 Thermal's water — not generic advice.
A basic carbon filter still helps
Thermal'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 Thermal 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 Thermal, CA tap water safe to drink?
Thermal's water quality earned a grade of D (48/100). Significant issues have been found. A water filter is strongly recommended. The city ranks #619 out of 690 cities tested in California.
What contaminants are in Thermal's water?
Lead was measured at 5.0 ppb (90th percentile). 1172 violations are on record.
How is Thermal'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 Thermal?
Based on current data, basic filtration should suffice for additional peace of mind.
Where does Thermal's water come from?
Thermal's water is sourced from Groundwater. The city has 17 water systems serving approximately 3,056 residents.
What health violations has Thermal's water system had?
Thermal has 127 health-based violations on record. The most recent violation was recorded in December 2025. Health-based violations mean the water exceeded EPA maximum contaminant levels (MCLs) for a regulated substance. 171 violations remain unresolved.
Is Thermal's groundwater at risk of contamination?
Thermal 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 1172 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 Thermal's water compare to other cities?
Thermal ranks #619 out of 690 cities in California (better than 10% of state cities) and #13265 out of 15382 cities nationally (14th percentile). The grade of D reflects the combined assessment of violation history, lead and copper levels, PFAS contamination, and regulatory compliance.