Costa Mesa Water Quality Guide: Mesa Water District Hardness, Chloramine, and What It Means for Your Home

Mesa Water District provides water service to about 110,000 residents in most of Costa Mesa, part of Newport Beach and some unincorporated areas. Its supply is local groundwater from the Orange County Groundwater Basin, supplemented by deep amber-tinted groundwater that is treated at the Mesa Water Reliability Facility. Imported water from the Metropolitan Water District is available as a backup supply. According to Mesa Water District's 2026 Consumer Confidence Report (2025 data), its groundwater averages 113 mg/L of hardness (6.6 grains per gallon), with results from 20.6 to 293 mg/L, and it is disinfected with chloramines. The amber color in the deep water comes from organic compounds left by ancient buried redwoods, not from iron, and it is removed before the water reaches customers.

Get a free water test for your Costa Mesa home. Call us at (949) 873-1129.

Where Costa Mesa water comes from

Mesa Water District's Consumer Confidence Report describes three parts to its supply:

• Orange County Groundwater Basin. Most of the supply is pumped from the basin beneath Costa Mesa. The basin is replenished with water from the Santa Ana River, the Groundwater Replenishment System and the Metropolitan Water District of Southern California. Mesa Water says about 85 percent of its supply comes from these shallower wells.
• Mesa Water Reliability Facility (MWRF). Deep wells, about 1,000 feet underground, pump water with an amber tint. Nanofiltration at the MWRF removes the color before the water is added to the supply. Mesa Water puts this deep water at about 15 percent of its supply.
• Imported water, as a backup. If needed, Mesa Water can import water from the Municipal Water District of Orange County, which delivers Metropolitan's State Water Project and Colorado River water.

Mesa Water District publishes the full report each year on its water quality page. The figures below come from the 2026 report, which covers 2025.

Costa Mesa water hardness: what the data shows

Mesa Water District's groundwater averaged 113 mg/L of total hardness as calcium carbonate in 2025, or 6.6 grains per gallon. Individual results ranged from 20.6 to 293 mg/L (1.2 to 17 grains per gallon).

The USGS classifies 0 to 60 mg/L as soft, 61 to 120 mg/L as moderately hard, 121 to 180 mg/L as hard and more than 180 mg/L as very hard (USGS Water Science School). By that scale the district average is moderately hard, and the range runs from soft to very hard. The report does not break the results down by neighborhood, which is why a reading at your own tap is more useful than the district average when you size a softener.

Mesa Water describes the deep amber water from the MWRF as naturally soft. The imported Metropolitan water the district can use as a backup is harder: the same report lists an average of 236 mg/L (14 grains per gallon) for it.

Source: Mesa Water District 2026 Consumer Confidence Report (2025 data), groundwater table, mesawater.org/water-quality. ND means not detected. Check the most recent report for current figures.

Mesa Water's report also states that the district does not add fluoride to its water; the fluoride listed above is naturally occurring.

Chloramine: what it means for your filter

Mesa Water District disinfects its groundwater with chloramines, a combination of chlorine and ammonia, before it enters the distribution system. Metropolitan's imported water is also treated with chloramines, according to the same report.

For Costa Mesa homeowners, chloramine affects filter selection. Many ordinary carbon filters, including many pitcher and refrigerator filters, are rated for chlorine taste and odor but not for chloramine. If you buy a filter to improve the taste of Costa Mesa water, check that its certification listing names chloramine reduction. Catalytic carbon is the media usually used for this.

Chloramine does not evaporate from water left standing the way free chlorine does. Mesa Water's report advises customers who keep fish ponds, tanks or aquariums to treat water for chloramines before use.

The amber water: organic color from ancient redwoods

Part of Mesa Water District's supply comes from a deep aquifer with amber-colored water. Mesa Water says the color comes from the remnants of redwood forests that grew along the Orange County coast more than 30,000 years ago and were buried over time, leaving organic compounds in the water (Mesa Water District, Tapping Into Our Ancient Supply).

The amber color is not iron. Mesa Water treats this water at the Mesa Water Reliability Facility with sand separators, cartridge filters and nanofiltration membranes, which remove the color before the water is delivered. The district describes the deep water as naturally soft and says it meets all drinking water quality standards. In its 2025 groundwater results, color was not detected on average, with a highest reading of 5 color units against a secondary standard of 15.

If you see orange or brown staining at your home, the source is more likely your own plumbing or fixtures than the district supply. A water test that includes iron will show whether iron is present at your tap. See the whole house water filtration page for Costa Mesa for treatment options.

PFAS monitoring in Costa Mesa

Mesa Water District's 2026 Consumer Confidence Report does not include a PFAS results table. Two public sources publish PFAS results for water systems:

• California State Water Resources Control Board: PFAS in drinking water
• EPA UCMR 5 data finder: epa.gov/dwucmr

Water softeners and ordinary carbon filters are not designed for PFAS. If PFAS reduction is a priority, a point-of-use reverse osmosis system whose certification listing names PFOA and PFOS reduction is the usual option. See the reverse osmosis systems page for Costa Mesa for what an RO system covers.

Choosing the right treatment for Costa Mesa water

Hardness: Mesa Water's groundwater averages 6.6 grains per gallon but ranges from 1.2 to 17, so the right answer depends on your tap. If your reading is in the hard or very hard range, a water softener addresses scale and soap use across the whole house. The water softeners page for Costa Mesa covers system sizing.

Chloramine: A whole house or under-sink filter certified for chloramine reduction handles the disinfectant at the tap.

Dissolved solids and taste: Total dissolved solids averaged 327 mg/L in 2025, with results up to 582 mg/L. A kitchen reverse osmosis system lowers dissolved solids in drinking and cooking water.

PFAS (if detected): A point-of-use reverse osmosis system addresses PFAS compounds that softeners and ordinary carbon filters do not.

Data in this article comes from Mesa Water District's 2026 Consumer Confidence Report (2025 data) and Mesa Water District's article on its deep amber water. Verify current results with the most recent report at mesawater.org/water-quality.