Brentwood Water Hardness & Quality Report (2026)

The City of Brentwood, California operates a mixed water system serving over 21,000 connections in Contra Costa County. The utility draws from six groundwater wells tapping local aquifers and surface water sourced from rivers in the Sierra Mountain Range that flow into the Sacramento–San Joaquin Delta. Water is treated at the City of Brentwood Water Treatment Plant before distribution. The 2024 Water Quality Report confirms compliance with all federal and state drinking water standards, and the utility continuously monitors pH balance to maintain water stability.

Brentwood's water originates from the Sacramento–San Joaquin Delta watershed and underlying Eocene-age alluvial deposits. The primary aquifer formations — Domengine and Markley — consist of sandstone and limestone deposited during ancient marine transgression, rich in calcium carbonate and magnesium sulfate. These ancient marine sedimentary rocks continuously leach dissolved minerals into both the groundwater and surface supplies, resulting in a naturally hard water supply with mineral character typical of Contra Costa County's geological heritage from prehistoric inland seas.

At hard hardness levels, scale buildup is visible on fixtures and inside appliances, with water heaters and dishwashers particularly affected by reduced efficiency and increased energy consumption. Soap consumption rises as lathering becomes more difficult. The utility's naturally noncorrosive groundwater minimizes lead and copper leaching — a benefit of high hardness. Many residents install water softeners or point-of-use treatment to protect appliances; historical data indicates past exceedances of hexavalent chromium and total trihalomethanes (TTHMs) above health advocacy guidelines, though the system remains within regulatory limits.