EPA system AZ0407095 · Arizona

Mesa City of: Lithium at or above EPA's 10 ppb health reference level

System ID AZ0407095; community water system; Arizona; source: surface water; serves 466,000 people via 142,500 connections; status: active

In focus466,000people served, EPA registry

Public records. Clearer context.

Mesa City of is a local-government-owned community water system in Arizona serving about 466,000 people, matched to 15 ZIP codes.

PFAS treatment declared to EPA: None declared (67 of 67 sampling events) · PFAS found before UCMR 5: Yes, at 67 of 70 sampling events

PFAS and lithium: what EPA's national survey found

EPA tested this water for 30 substances and found 4. Lithium reached 525 ppb; EPA's health reference level, which is guidance and not a limit, is 10 ppb.

Between February 2023 and November 2025, EPA's UCMR 5 program tested 2,100 samples from 31 sampling locations for 30 contaminants (29 PFAS plus lithium). 4 were detected above the reporting level in at least one sample. Lithium reached 525 ppb in a single sample, at or above the health reference level of 10 ppb, which is non-regulatory.

Sampling-point average: mean of a location's two (ground water) or four (surface water) UCMR 5 results with non-detects counted as zero, EPA's method for comparing UCMR 5 data to the PFAS MCLs. EPA rounds to the reference value's significant digits before deciding whether an average is "greater than" an MCL (PFOA/PFOS averages count as above 4.0 ng/L only from 4.05 ng/L; lithium results count as above the 10 ppb reference only from 15 ppb). This site does not apply that rounding: "at or above" here means the measured value is numerically at or above the reference.

Utility-reported context (UCMR 5 questionnaire, aggregated across sampling events): PFAS previously found at this system: yes at 67 of 70 sampling events, not known at 3 of 70 sampling events; potential PFAS sources nearby: not known at 67 of 70 sampling events, no at 3 of 70 sampling events; PFAS treatment in place: no PFAS treatment at 67 of 67 sampling events.

Lead at customer taps

In the latest completed monitoring period, ending Dec 31, 2024, 9 in 10 sampled homes had lead at or below 5.0 ppb, below the 15 ppb action level that triggers utility action. None of the 12 periods on record reached it.

In the most recent completed lead monitoring period, ending Dec 31, 2024, the 90th-percentile lead result at customer taps was 5.0 ppb, below the action level of 15 ppb (12 monitoring periods on record, none at the action level). The 90th percentile is the value that 9 in 10 sampled homes were at or below. Values are in parts per billion (ppb).

Drinking water violations since Sep 3, 2016

EPA lists 91 violations since Sep 3, 2016. None is health-based. All concern missed monitoring, reporting or public notices, not the water itself.

EPA's SDWIS database lists 91 violations recorded since Sep 3, 2016: 91 for monitoring or reporting, none health-based.

Sanitary surveys and site visits

Most recent state inspection: Nov 20, 2025 (reason not recorded); 10 visits since Sep 3, 2021.

What you can do about these results

ZIP codes served

Sources

Data vintage: EPA UCMR 5 occurrence data, samples collected 2023-01-03 – 2026-06-17, final release, August 2026 (file dated Aug 28, 2026); EPA SDWIS via ECHO, 2026Q2 extract (file dated Jul 9, 2026); EPA service-area boundaries v3.0; Census 2020 ZCTAs. Page generated 2026-09-03.

• EPA ECHO detailed facility report
• EPA UCMR 5 Data Finder
• EPA service-area boundary: modeled, 145.1 sq mi