MyTapWater.us

PWSID CA2210002

PONDEROSA BASIN MUTUAL WTR CO

Community water system based in Mariposa, CA

Service area on file with EPA: Mariposa County. EPA's recorded service area can be incomplete for regional authorities. The cities and counties above are what the utility has filed with EPA; the utility may serve additional areas.

Population served
798
Source
Groundwater
Status
Active

At a glance

1 issue above the federal safety limit

Risk classification follows EPA's published values for safe drinking water, with caution and concern bands reviewed by a clinician. Past resolved violations do not influence this card. See methodology.

Lead service line inventory

Utility reports no confirmed lead service lines

PONDEROSA BASIN MUTUAL WTR CO reports 0 confirmed lead service lines, 314 non-lead, 0 unknown (total 314) in the EPA SDWIS service line inventory (2026Q1).

  • 0 confirmed lead service lines
  • 0 galvanized requiring replacement (LCRI treats these as lead)
  • 0 unknown (0.0% of total)
  • 314 confirmed non-lead (100.0%)
  • 314 total service lines in the system
What to do if your service line might be lead
  1. Ask your utility to check the service-line classification for your specific address. Many utilities provide a public address-lookup tool linked from the inventory page.
  2. Get on the replacement queue. Under the LCRI, utilities must replace all lead and galvanized-requiring- replacement lines within 10 years (clock generally starts November 2027). Some prioritize requests.
  3. Until the line is replaced: flush the tap 30 seconds after long stagnation, use cold water for drinking and cooking, and consider an NSF/ANSI 53 lead-rated tap filter.
  4. Talk to your clinician about a blood lead test for anyone in the home, especially a pregnant person or a child under 6. Lead in drinking water guide.

Inventory data sourced from PONDEROSA BASIN MUTUAL WTR CO ( retrieved May 24, 2026 ; curator confidence: high ). Confirmed against the original source automatically each month; see methodology.

Lead and copper test results

The most recent measurement per contaminant from EPA's Lead and Copper Rule sampling.

Why only lead and copper, and not arsenic, nitrate, or others?

EPA's bulk SDWIS download is the only nationwide per-system sample data they publish, and it only includes the Lead and Copper Rule table. Values for other regulated contaminants (TTHMs, nitrate, arsenic, etc.) appear on this page only when they trigger a violation. For the full per-system contaminant suite, see the utility's annual Consumer Confidence Report (link further down the page).

Most recent measurements per contaminant (Lead and Copper Rule) . Sorted by risk: concern first, then caution, then unrated, then safe.
Contaminant Most recent Date Risk
Lead
PB90
 0 mg/L December 31, 2025 Below regulatory thresholds

Data from EPA SDWIS (Lead and Copper Rule sample table) , last refreshed May 24, 2026.

PFAS and emerging contaminants

This system was tested 120 times under EPA's latest PFAS monitoring program; 1 of the 30 chemicals tested was detected.

What is this testing program?

EPA's fifth Unregulated Contaminant Monitoring Rule cycle (UCMR 5, 2023 to 2025) required every public water system serving over 3,300 people to test for 29 per- and polyfluoroalkyl substances (PFAS) plus lithium; 30 chemicals in total. Most recent detection per chemical shown below.

Most recent UCMR 5 detection per contaminant . Sorted by risk: concern first, then caution, then unrated, then safe.
Contaminant Most recent detection Date Risk
lithium
0.108 mg/LJuly 29, 2025 Concern
Tested but not detected (29 contaminants)

EPA tested for these substances and every sample was below the minimum reporting level. Absence of detection does not mean true zero; it means below the laboratory's quantitation threshold.

Data from EPA UCMR 5 (Unregulated Contaminant Monitoring Rule) , last refreshed May 24, 2026.

Fluoride

Per CDC My Water's Fluoride

PONDEROSA BASIN MUTUAL WTR CO reports mixed fluoridation across its water sources.

CDC's My Water's Fluoride listing marks this system as Mixed: it draws on multiple sources with different fluoridation statuses, or fluoridates only part of its service area. The annual water quality report for your specific service address has the most reliable measured concentration.

Source: CDC My Water's Fluoride, listed under Ponderosa Basin Mutual Wtr Co (Mariposa County). Verify on CDC's site .

Area context

Mariposa County, CA (2020 data)

Community water systems
1 of 15 add fluoride
Population on fluoridated water
1,883 of 6,044 (31.2%)

California statewide (2020 data)

Population on fluoridated water
21,879,582 of 38,051,212 (57.5%)
Community water systems adding fluoride
417 of 3,057

Data from CDC My Water's Fluoride (per-system status) , last refreshed May 19, 2026.

Data from CDC Water Fluoridation Reporting System (state and county aggregates) , last refreshed May 16, 2026.

Compliance history

EPA-recorded violations against this system over the last 5 years.

How to read this section

Health-based violations are when a measured limit was exceeded; the measured concentration is shown alongside the EPA federal limit where SDWIS published it. Monitoring and reporting items are paperwork issues (missed sample dates, late filings) that do not themselves indicate unsafe water.

No health-based violations

No health-based violations on file in the last 5 years. EPA recorded 1 monitoring or reporting item (paperwork) during the same period.

1 monitoring and reporting item (paperwork) , 1 still open · these are not health risks
Monitoring and reporting items in the last 5 years
Period start Relates to Item Status
October 1, 2024 Lead and Copper Rule Follow-up Or Routine LCR Tap M/R Addressed

Data from EPA SDWIS (violation records) , last refreshed May 24, 2026.

Where to see every contaminant this utility tested for

EPA's bulk SDWIS dataset gives MyTapWater.us per-system measured values for lead and copper, plus violation records for everything else. To see every regulated contaminant this utility tested for in the past year (TTHMs, HAA5, nitrate, arsenic, fluoride, chromium, etc.) with measured values, read the utility's Consumer Confidence Report (CCR).

Every community water system is required by EPA to publish a CCR annually, by July 1, listing every contaminant they sampled, the measured value, the federal limit, and any health-based exceedances. Most utilities post the report online; some mail it with your bill.

How to find PONDEROSA BASIN MUTUAL WTR CO's CCR:

Other water systems in Mariposa County, CA

Compare nearby utilities by population served.

Contact this utility

Public administrative contact information for this water system, as filed with the EPA. Use this to ask about your service line, request your home's lead status, or report a water quality issue.

Administrator
DONATI, ALEARDO TUFFY
Phone
209-742-6572
Email
tnpdonati@gmail.com
Mailing address
5623 PARKER DRIVE
MARIPOSA, CA 95338

Where this page's data comes from

Bundle released 2026-Q2, regenerated May 24, 2026. Each section above also shows its own source date so you can tell at a glance how fresh that part of the page is.

Every value on this page is cross-verified before publication; read our methodology for the verification steps and corrections process.