Atherton, CA Water Safety: 65/100 (2026)
1 ZIP code · 1 water system · Updated 2026-06-03
Atherton water quality is uneven — some service areas show clean compliance; others carry documented violations in CA EPA records.
How Atherton Compares
Data: EPA SDWIS Last verified: 2026-06-03
Atherton Water: The Quick Version
- Homes built before 1986: 68% — older plumbing may contain lead solder.
- Estimated remediation: $1,800 per household.
- CDC health risk index: 9.58.
Water Systems Serving Atherton
The structure of water supply in Atherton, CA is straightforward: one utility provides the bulk of residential service among 1 tracked system, concentrating rate-setting and infrastructure decisions under a single organization.
Overview
We track water quality and home safety data for 1 ZIP code in Atherton, California (population ~7,030), covering 1 community water system serving approximately 22,362 people region-wide.
No EPA violations recorded across any ZIP codes in Atherton — an excellent indicator of water quality.
Home Safety Score
Average Home Safety Score for Atherton: C (65/100)
The score combines three factors:
| Factor | What It Measures |
|---|---|
| Water Quality | EPA violations and compliance history |
| Lead Levels | 90th percentile lead concentration vs EPA action level |
| Radon Risk | EPA radon zone classification |
Water Sources
Atherton water systems draw from: Surface water.
Lead & Copper
- Lead data: not yet available for Atherton
- 0 ZIP codes exceed the EPA lead action level
Radon Risk
Dominant radon zone: Zone 3 (Low Risk)
Areas with No Violations
| ZIP Code | Safety Score | System | Population |
|---|---|---|---|
| 94027 | C | MENLO PARK MUNICIPAL WATER | 22,362 |
All ZIP Codes in Atherton
- 94027 [C]
Data Sources
- Water quality: EPA Safe Drinking Water Information System (SDWIS)
- Lead/copper: EPA Lead and Copper Rule sampling data
- Radon: EPA Map of Radon Zones
Updated daily.
CDC Health Data for Atherton
Source: CDC PLACES (County-level estimates). Water contamination can correlate with respiratory and chronic health conditions.
Compared to National Average
Vertical line = national average. ■ Above national · ■ Below national
How Old Is Atherton's Housing Stock?
With 68% of homes built before 1986, lead solder in plumbing is a potential concern. The EPA banned lead solder in 1986, but many older homes retain original plumbing.
Source: U.S. Census Bureau American Community Survey (ACS).
Housing Age Profile
When a city's housing median build year is 1969, as in Atherton, the implication for water quality research is straightforward: municipal-level data captures what leaves the treatment plant, but household plumbing from before 1986 determines what actually arrives at the tap. In cities where older housing predominates, that gap between system-level and household-level data is widest.
Over half of homes in Atherton were built before 1986, when lead solder was banned. Older plumbing may leach lead into drinking water, especially with corrosive water chemistry.
Source: U.S. Census Bureau ACS B25034.
Atherton: Remediation Cost in Perspective
Given current Atherton valuations, the remediation-to-property-value ratio is low — most homeowners are looking at a proportionally modest share that fits within routine financial planning.
Remediation costs in Atherton are relatively low compared to home values. The $1,200–$2,500 estimated range is a small fraction of median property value. Home values are 171% above the California average.
Protecting Children from Lead in Atherton
Why children are most at risk: The CDC states there is no safe level of lead exposure for children. Children under 6 absorb lead more readily than adults, and even low levels can cause developmental delays, learning difficulties, and behavioral problems.
After the federal action removing lead-bearing solder from new plumbing took effect, building practice shifted — but 68% of the Atherton inventory predates that line. With aggregate samples near or beyond 0.015 mg/L, an in-home check moves out of the optional column into the standard list.
Sources: EPA Lead and Copper Rule, U.S. Census Bureau ACS, CDC childhood lead poisoning prevention guidelines.
Climate-Related Water Risk for Atherton
Measured across the NFIP's multi-decade tracking period, Atherton shows a moderate flood record — 13 claims and 100% of ZIP codes carrying FEMA flood zone status. For water quality, that combination matters because flood events at this frequency can periodically stress infrastructure: treatment plants, private wells, and distribution systems all face elevated risk during significant flooding.
Atherton has a moderate flood history with 13 FEMA claims averaging $28,968 per payout. 100% of ZIP codes fall within FEMA flood zones. Flood events can contaminate drinking water and overwhelm treatment systems.
How flooding affects water quality: Flood events can introduce sewage, agricultural runoff, and industrial chemicals into water supplies. Even after floodwaters recede, contamination can persist in wells and aging infrastructure. Flood damage can add significantly to the estimated <strong>$1,800</strong> remediation cost per household.
Residents in flood-prone areas should consider flood insurance even outside FEMA zones — over 25% of flood claims come from low-to-moderate risk areas. After any flood event, test your water before drinking.
Source: FEMA National Flood Insurance Program (NFIP) claims data, FEMA flood zone designations.
What You Can Do in Atherton
- Test your water at home. City-level data shows averages — your tap may differ. NSF-certified test kits cost $20-40 and give results in days.
- Install a certified water filter. An NSF-certified pitcher or under-sink filter removes most common contaminants.
- Check your home's plumbing. With 68% of homes built before 1986, lead solder is a real possibility.
Deep Dive Reports
Detailed analysis for Atherton, CA