Updated November 1, 2026

Fresno's water is a story about individual wells

Fresno serves more than 550,000 people across a 114-square-mile service area, using surface water treatment plants and about 260 groundwater wells. San Joaquin Valley farm history shows up in that groundwater. The report averages the data system-wide, but its footnotes name individual wells by street corner.

Wells taken out of service

Pulling a well is how the system keeps averages low. In 2025, 1,2,3-trichloropropane (TCP), an industrial and pesticide byproduct, averaged 0.45 ng/L against a 5 ng/L limit, though one well reached 5.2. Nitrate averaged 4.80 mg/L, with a high of 12 at the well later cleared as a lab error.

PFAS at the well level

Fresno is testing for 29 PFAS compounds. System averages are low, but the ranges reveal hot spots:

• PFOA averaged 1.33 ng/L, with a high of 13.
• PFOS averaged 1.58 ng/L, with a high of 24.
• PFHxS averaged 0.91 ng/L, with a high of 38.
• PFBS averaged 0.46 ng/L, with a high of 7.

Wells that exceeded the new federal standards during quarterly testing were taken out of service. If you live near a well that has had problems, a point-of-use filter certified for PFAS is a reasonable hedge. Our filter selector covers the certifications, and the RO output and waste calculator sizes an under-sink system.

Other groundwater constituents

Arsenic averaged 3.15 µg/L (up to 5.1), hexavalent chromium 2.50 µg/L (0.1–9.6, just under California's 10 µg/L limit), and gross alpha 3.73 pCi/L. Solvents linked to dry cleaners and degreasers also appear at low levels: PCE averaged 0.07 µg/L and TCE 0.32 µg/L. Because most of the supply is groundwater with only chlorine residual, disinfection byproducts are very low, with TTHM averaging 0.18 µg/L and HAA5 4.30.

Hardness and recharge

Hardness averages 129 mg/L (about 7.5 gpg) and dissolved solids 187 mg/L. That's enough to scale water heaters over time. The hardness converter handles the unit math.

Groundwater is what the city calls its “savings account.” The Leaky Acres and Nielsen recharge basins cover 304 acres and let water soak back into the aquifer. Fresno has also won $10.4 million in state drought grants, including $5.24 million for Leaky Acres improvements and $5.14 million to expand its Lawn to Garden program.