Is Modesto tap water safe to drink?

Modesto, City of uses free chlorine, according to its own water quality reporting. Free chlorine is the easy case: almost any carbon filter, from a basic pitcher to a shower filter, reduces the taste and smell.

Modesto's water measures about 2.6 grains per gallon (45 mg/L as calcium carbonate), which is soft on the US Geological Survey scale: soft below 60 mg/L, moderately hard 60-120, hard 120-180, very hard above 180.

At this level a water softener is usually not worth the cost. Spend on filtration for taste or specific contaminants instead.

Hardness data: TapWaterData Water Hardness Dataset (tapwaterdata.com), licensed CC BY 4.0. Underlying source: Utility-reported water quality data — MODESTO, CITY OF (PWSID CA5010010), 2025-04-21.

In Modesto, City of's most recent lead sampling, for the period ending December 2027, 90% of tested homes came in at or below 12 ppb of lead. That is below EPA's current 15 ppb action level but above the 10 ppb level that takes effect in November 2027.

This is a system-wide statistic, not a reading of your tap. Lead comes from lead service lines, old solder and some brass fixtures inside homes, so two houses on the same street can differ. Testing your own tap costs $15-40, and many utilities test free on request.

EPA's lead action level is 15 parts per billion (ppb) today and drops to 10 ppb in November 2027 under the Lead and Copper Rule Improvements. FDA's limit for bottled water is 5 ppb. EPA's health goal for lead is zero.

In EPA's 2023-2025 sampling of Modesto, City of, these PFAS were detected: PFOS up to 26 ppt (2024 limit 4); PFHxS up to 9.3 ppt (2024 limit 10); PFOA up to 8.6 ppt (2024 limit 4); PFBS up to 4.3 ppt (no federal limit). PFOS and PFOA were measured above the 2024 limit in at least one sample. These are the highest single results; utilities are judged on running annual averages, so a high sample is not by itself a violation.

Reverse osmosis is the most reliable home treatment for PFAS. Some carbon filters are certified for PFOA and PFOS reduction under NSF/ANSI 53; check the product listing for that claim, not just the word PFAS on the box.

In April 2024 EPA set enforceable limits of 4 parts per trillion (ppt) for PFOA and PFOS, and 10 ppt for PFHxS, PFNA and HFPO-DA (GenX). In May 2025 EPA said it intends to keep the PFOA and PFOS limits, extend the compliance deadline to 2031, and rescind the other three. We compare results to the 2024 limits and label which ones may change.

Modesto, City of has no health-based violations on file with EPA since 2016.

Modesto is in Stanislaus County, which EPA places in Radon Zone 3: the predicted average indoor level is below 2 pCi/L.

Zone describes a county average. Individual homes in every zone test high, so EPA recommends testing every home, especially basements and ground floors. Fix at 4 pCi/L or above.

EPA radon zones describe counties, not houses. Zone 1 counties have a predicted average indoor level above 4 picocuries per liter (pCi/L), Zone 2 between 2 and 4, Zone 3 below 2. Homes with high levels are found in every zone, which is why EPA recommends that every home be tested, and fixed at 4 pCi/L or above. See every California county's radon zone.