Normal days
Local groundwater from nine wells and the Reliability Facility. Average 6.6 gpg, moderately hard.
Homeowner guide
Costa Mesa water hardness and amber water, by the numbers
Mesa Water District's 2026 water quality report puts Costa Mesa's local groundwater at an average hardness of 113 mg/L, about 6.6 grains per gallon. That is moderately hard, not the 16 to 18 grains some websites claim.
Call (657) 669-4766Request service
Written and fact-checked by John, editor, MBA in marketing
Updated against City, utility and state sources
Quick answer
Costa Mesa tap water from Mesa Water District averaged 113 mg/L of hardness in 2025 data, about 6.6 grains per gallon, with a range of 20.6 to 293 mg/L (about 1.2 to 17 grains). The USGS calls 61 to 120 mg/L moderately hard. Imported backup water is harder, about 14 grains on average. Homes on IRWD water should check IRWD's own report.
- Local groundwater
- 113 mg/L average (6.6 gpg)
- Measured range
- 20.6 to 293 mg/L
- Imported backup
- About 14 gpg average
- USGS class
- Moderately hard
What Mesa Water's 2026 report says about Costa Mesa water hardness
Mesa Water District's 2026 Consumer Confidence Report, which covers 2025 test data, lists local groundwater hardness at an average of 113 mg/L, or 6.6 grains per gallon.
Every California water system has to publish a yearly Consumer Confidence Report, often called the CCR or water quality report. We opened Mesa Water's 2026 edition ourselves and copied the numbers below straight from its tables. Mesa Water serves about 110,000 residents across most of Costa Mesa, part of Newport Beach and some unincorporated areas, so for most homes from Mesa Verde to the Eastside, this is the report that describes the water in your pipes.
The report splits results into two columns. The first is Mesa Water's local groundwater, which is what the district delivers almost all the time. The second is imported water from the Metropolitan Water District of Southern California, treated at Metropolitan's Diemer and Weymouth plants. Mesa Water describes its supply as 100% local, drawn from nine wells plus the Mesa Water Reliability Facility, and treats imported water as a backup.
| Constituent | Local groundwater, average | Local groundwater, range | Imported backup water, average |
|---|---|---|---|
| Total hardness (mg/L as CaCO3) | 113 | 20.6 to 293 | 236 (Diemer), 234 (Weymouth) |
| Total hardness (grains per gallon) | 6.6 | 1.2 to 17 | 14 (range 11 to 16) |
| Calcium (mg/L) | 33 | 7.5 to 86 | 56 |
| Magnesium (mg/L) | 6.7 | Not detected to 19 | 22 |
| Sodium (mg/L) | 72.7 | 23 to 184 | 88 to 89 |
| Total dissolved solids (mg/L) | 327 | 150 to 582 | 545 (Diemer), 536 (Weymouth) |
| pH (units) | 8.2 | 7.8 to 8.7 | 8.2 to 8.3 |
| Color (color units, limit 15) | Not detected | Not detected to 5 | 1 |
| Fluoride (mg/L) | 0.46 | 0.26 to 0.76 | 0.7 |
A few lines in the report matter for plumbing beyond hardness itself:
- Disinfectant. Mesa Water uses chloramines, a mix of chlorine and ammonia. The distribution system chlorine residual averaged 2.07 mg/L in 2025, with a range of 0.19 to 2.78.
- Fluoride. The report says Mesa Water does not add fluoride. The small amount in local groundwater is natural, and the fluoride in imported water comes from Metropolitan's treatment.
- Service lines. Mesa Water completed its first service line inventory in 2024 under the U.S. EPA's Lead and Copper Rule Revisions and found no lead or galvanized service lines that require replacement in its system. That covers the district's lines, not the pipes inside your house.
Hardness is not a health problem. It is about minerals: mostly calcium and magnesium, measured together and reported "as calcium carbonate." What hardness does affect is scale inside water heaters, tankless units, faucet aerators, shower heads and toilet valves, which is why a plumber cares about it.
How to convert mg/L to grains per gallon
Divide mg/L (or ppm) of hardness by 17.1 to get grains per gallon, which is the unit water softener makers use.
Water reports use milligrams per liter, which is the same as parts per million for water. Softener sizing charts and test strips often use grains per gallon, written gpg. Mesa Water's report gives both, and its own pair of numbers shows the ratio: 113 mg/L becomes 6.6 gpg. One grain per gallon equals about 17.1 mg/L.
The U.S. Geological Survey sorts water into four plain classes by hardness as calcium carbonate. We added grains so you can compare a test strip, a softener brochure and the CCR without doing the math.
| mg/L as CaCO3 | Grains per gallon | USGS class | Costa Mesa reference point |
|---|---|---|---|
| 0 to 60 | 0 to 3.5 | Soft | Low end of Mesa Water's groundwater range (20.6 mg/L, about 1.2 gpg) |
| 61 to 120 | 3.6 to 7.0 | Moderately hard | Mesa Water local groundwater average (113 mg/L, 6.6 gpg) |
| 121 to 180 | 7.1 to 10.5 | Hard | Some individual well results fall here |
| More than 180 | More than 10.5 | Very hard | Imported Metropolitan water (about 234 to 236 mg/L, 14 gpg); top of groundwater range (293 mg/L, about 17 gpg) |
Two quick conversions people ask us about
- A test strip reading of 120 mg/L is about 7 grains per gallon, right at the line between moderately hard and hard.
- A softener brochure that says "sized for 15 grains" is describing water near 257 mg/L, which is close to Metropolitan's imported water and far above Mesa Water's local average.
Why some sites say Costa Mesa water is 16 to 18 grains
The 16 to 18 grain figure does not match Mesa Water's measured average; the report shows 6.6 grains for local groundwater and about 14 grains for imported backup water.
When we looked at what other plumbing and water treatment websites say about Costa Mesa, one large national brand claims the city's water runs 16 to 18 grains per gallon. We do not know how that figure was produced, and the page does not cite the Mesa Water report. Here is what the published numbers actually show, so you can judge it yourself.
- The local average is 6.6 grains. That is less than half of 16 grains.
- The highest local result is about 17 grains. The top of the groundwater range, 293 mg/L, converts to about 17 gpg. That is a maximum reading, not what a typical home sees.
- Imported water averages 14 grains. Metropolitan's water ranges from 11 to 16 gpg. Even the top of that range does not reach 18.
Our best guess is that some sites lean on regional figures shaped by imported water, which is harder, or quote the top of a range as if it were normal. Either way, a softener sized for 16 to 18 grains in a Mesa Water home would be sized for water you probably do not have.
There is a fair caveat. Mesa Water blends output from several wells, and the report shows a wide range. A home near one source can see different water from a home across town, and conditions change when imported backup water is in use. If you want to know your own number, test it, using the steps further down this page.
Why hardness can change at your Costa Mesa tap
Hardness at your tap changes because Mesa Water blends several wells, and because imported backup water is much harder than local groundwater.
The spread in the report, from 20.6 to 293 mg/L, tells you that not every well delivers the same water. Shallow and deep parts of the groundwater basin carry different minerals. The deep amber water treated at the Mesa Water Reliability Facility, described in the next section, is one source in the blend. The nine wells are others.
Then there is backup water. Mesa Water keeps a connection to Metropolitan's imported supply. When imported water is used, hardness jumps toward 14 grains and total dissolved solids rise to roughly 536 to 545 mg/L, compared with 327 mg/L for local water. If you ever notice more spotting on glass shower doors for a stretch, a change in source is one possible reason.
Individual wells
Results run from about 1.2 to 17 gpg depending on the source, so the blend at your address can differ from the average.
Backup water
Imported Metropolitan water averages about 14 gpg, which the USGS scale calls very hard.
Inside the house, hot water makes scale worse. Heating water drives calcium out of solution, which is why the bottom of a tank water heater collects sediment even on moderately hard water, and why tankless heat exchangers need descaling on a schedule. Cold water lines rarely scale badly at these levels.
Amber water and the Mesa Water Reliability Facility
Some of Costa Mesa's deep groundwater is naturally amber colored from ancient redwood roots, and the Mesa Water Reliability Facility removes that color with nanofiltration before it reaches your tap.
People who hear "amber water" sometimes worry it means rust or a pipe problem. It does not. Mesa Water says the color comes from ancient redwood trees that grew along the Orange County coast more than 30,000 years ago. Their buried roots in the lower groundwater basin tint the water a tea-like amber.
The Mesa Water Reliability Facility, at the district's campus on Placentia Avenue, was built to use that water. It pulls from two deep wells at about 1,000 feet underground, stores water in a one-million gallon reservoir and runs it through nanofiltration, which removes the organic color. Sand separators and other filters handle inorganic material. Mesa Water says about 98 percent of the water that enters the facility is delivered as drinking water.
This facility is a big reason Mesa Water can say it is the only water district in Orange County that meets its demand entirely from local groundwater. The finished water's color in the 2026 report averaged "not detected," with a high of 5 color units against a limit of 15.
- 30,000+ years ago
Coastal redwoods
Redwood forests grow along the Orange County coast. Their roots later sit in the deep groundwater basin and tint it amber.
- 2013
Reliability Facility opens
Mesa Water opens the facility with two deep wells and nanofiltration to remove the amber color.
- 2024
Service line inventory
Mesa Water completes its first service line inventory and finds no lead or galvanized service lines needing replacement in its system.
- 2026
Current report
The 2026 CCR reports 2025 data: local groundwater hardness 113 mg/L average, color not detected on average.
Costa Mesa homes on IRWD water
Parts of Costa Mesa get water from the Irvine Ranch Water District instead of Mesa Water, and those homes should read IRWD's own water quality report.
IRWD's 2026 Water Quality Report, which covers 2025 results, says the district serves parts of Newport Beach, Tustin, Costa Mesa, Orange and unincorporated Orange County. It does not list which Costa Mesa neighborhoods, and we will not guess. The simple way to know is your water bill. If it says Mesa Water District, the numbers above apply. If it says Irvine Ranch Water District, use IRWD's report. Our who to call guide explains other ways to tell.
IRWD's supply is a blend of local groundwater, local surface water and imported water. IRWD's report notes that because of that blend, customers may notice a difference in taste or hardness at different times of the year, and that this does not affect safety. It also says the white deposits hard water leaves on fixtures can be removed with a simple vinegar solution, and that hard water is not a threat to health.
We tried to pull IRWD's hardness figures from the online version of its report, but the results table did not come through clearly enough to tell which number belongs to which source. Rather than print a number we cannot stand behind, we suggest IRWD customers open the report themselves or call IRWD at 949-453-5300 and ask for the hardness of the water serving their address.
What moderate hardness means for water heaters and fixtures
At about 6.6 grains, Costa Mesa water causes slow, manageable scale: tank heaters collect sediment, tankless units need periodic descaling, and aerators and shower heads clog over time.
Moderately hard water is not a crisis, but it is not nothing. Here is how it shows up in the 1960s and 1970s homes that make up about half of Costa Mesa's housing, and in the apartments that house many of the city's renters.
| Fixture | What you notice | What helps |
|---|---|---|
| Tank water heater | Popping or rumbling, slower recovery, sediment when the drain valve is opened | Periodic flushing; a plumber can check the anode and drain valve |
| Tankless water heater | Error codes, fluctuating temperature, lower flow at the tap | Descaling the heat exchanger on the maker's schedule; isolation valves make it easier |
| Faucet aerators and shower heads | Weak or uneven spray, white crust | Unscrew and soak in vinegar; replace worn aerators |
| Toilet fill valves and flappers | Running toilet, slow refill | Replace the fill valve or flapper; see our toilet and faucet repair page |
| Glass, tile and dishes | White spots that wipe off with vinegar | Squeegee showers, rinse aid in the dishwasher |
Tank water heaters
The U.S. Department of Energy says tank water heaters typically last about 10 to 15 years with proper maintenance. Scale is one of the things that wears them down. As calcium settles to the bottom, the burner or element heats through a layer of sediment, which is noisier and less efficient. Flushing a few gallons from the drain valve once in a while helps. On an older tank, though, an old plastic drain valve can stick or leak after it is opened, so ask a plumber if you are unsure. If your heater is near the end of its life, our water heater repair and replacement page covers repair versus replace and the City of Costa Mesa installation rules.
Tankless water heaters
Tankless units heat water fast through a narrow heat exchanger, which makes them more sensitive to scale than a tank. On Mesa Water's local supply, descaling on the manufacturer's schedule is usually enough. Homes that see a lot of imported backup water, or that sit near a harder well, may need it more often. Our tankless water heater page explains descaling and service valves.
Published cost ranges
Angi's published estimate for a tank water heater replacement is $600 to $2,500 installed (2025), and its estimate for a tankless installation is $1,404 to $3,901 (2026). Those are national ranges, not quotes. Call (657) 669-4766 for an exact written quote for your home before any work starts.
Is a water softener worth it in Costa Mesa?
For most Mesa Water homes at about 6.6 grains, a whole-house softener is optional rather than necessary; it makes the most sense for tankless owners, people who hate spotting, or homes that test harder than average.
A salt-based softener swaps calcium and magnesium for sodium through ion exchange. It does stop scale. It also adds a brine tank, salt purchases, a drain connection and some upkeep. Whether that trade is worth it depends on your water and your fixtures, not on a sales pitch built around 16 to 18 grains.
Probably worth it
- You have a tankless water heater and want fewer descaling visits
- Your own test shows hardness well above the 6.6 grain average
- You are bothered by spotting on glass showers and fixtures
- You are already replumbing the main line, for example during a repipe, so the loop is easy to add
Probably not needed
- You have a tank heater and are fine flushing it now and then
- You rent and cannot alter the main water line
- Someone in the house is watching sodium intake
- The only reason offered is a hardness number without a source
Sodium and softened water
Mesa Water's local groundwater already carries an average of 72.7 mg/L of sodium, with a range of 23 to 184. A salt-based softener adds more, roughly in proportion to the hardness it removes. Many households keep one unsoftened cold tap in the kitchen for drinking and cooking. If sodium is a concern for someone in your home, ask a doctor before softening drinking water.
Alternatives to a full softener
- Point-of-use scale filters. Small cartridges that protect one appliance, such as a tankless heater or an espresso machine.
- Routine maintenance. Flushing a tank heater, descaling a tankless unit and soaking aerators in vinegar handles most of what moderate hardness does.
- Drinking water filters. These address taste and chloramine, but most do not soften water.
Permits for softeners
"Water Softener" appears as its own work type on the City of Costa Mesa plumbing permit application, alongside water heaters and repipes. If a softener is being plumbed into your main line, ask the installer whether a permit will be pulled. Our Costa Mesa plumbing permit guide explains how permits work through the City's TESSA system.
How to find your own water hardness
The fastest way to know your hardness is to check which district serves you, read that district's report, and confirm with an inexpensive test at the tap.
Check your bill
Find the water provider's name. Mesa Water District and Irvine Ranch Water District both serve parts of Costa Mesa, and their water differs.
Read the right report
Mesa Water customers can use the numbers on this page. IRWD customers should open IRWD's 2026 Water Quality Report or call 949-453-5300.
Test cold water at the kitchen tap
Use a hardness test strip or kit on cold water that has run for a minute. Hot water can read differently after passing through the heater.
Convert the result
Divide mg/L by 17.1 to get grains per gallon, then compare with the table above.
Ask Mesa Water if something looks off
For unusual color, taste or a reading far from the report, call Mesa Water's water quality line at 949-574-1031.
If you are weighing a softener or a tankless heater, or your water heater is making noise, we are glad to look at the whole picture. A plumber can tell you what the scale inside your fixtures says about your water, which is often more useful than any single number. Homes in neighborhoods like Mesa Verde, where many houses still have original 1960s plumbing, often have older shutoff valves and fixtures that scale has worn down over decades.
Water where it shouldn't be? Call now.
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Questions Costa Mesa homeowners ask
How hard is the water in Costa Mesa?
Moderately hard. Mesa Water District's 2026 report lists local groundwater at an average of 113 mg/L, about 6.6 grains per gallon, with a range of 20.6 to 293 mg/L. The USGS classifies 61 to 120 mg/L as moderately hard.
Is Costa Mesa water really 16 to 18 grains?
Not according to Mesa Water's own report. The local groundwater average is 6.6 grains, the highest local reading is about 17 grains, and imported backup water averages about 14 grains. A 16 to 18 grain claim does not match any average in the 2026 report.
Why is some Costa Mesa groundwater amber?
Ancient redwood roots in the deep groundwater basin tint the water amber. The Mesa Water Reliability Facility, opened in 2013, removes that color with nanofiltration, so finished tap water should not look amber.
Do I need a water softener in Costa Mesa?
Usually not, if you are on Mesa Water's local supply and have a tank water heater. A softener makes more sense for tankless owners, homes that test harder than the 6.6 grain average, or people bothered by spotting.
How do I convert mg/L of hardness to grains per gallon?
Divide by 17.1. For example, Mesa Water's average of 113 mg/L divided by 17.1 is about 6.6 grains per gallon.
Is hard water in Costa Mesa safe to drink?
Yes. Hardness is calcium and magnesium, and IRWD's report notes hard water is not a threat to human health. It mainly affects scale in water heaters, faucets and shower heads.
Does IRWD water in Costa Mesa have the same hardness as Mesa Water?
Not necessarily. IRWD blends groundwater, surface water and imported water, and says hardness can vary through the year. Check your bill, then read IRWD's 2026 report or call 949-453-5300.
Does hard water shorten water heater life?
Scale is one factor. The Department of Energy says tank heaters typically last 10 to 15 years with proper maintenance. Flushing sediment helps. If yours is noisy or slow, see our water heater repair page.
Sources
Facts on this page come from these public sources, checked November 1, 2026.
- Mesa Water District 2026 Consumer Confidence Report (2025 data)
- Mesa Water District: Mesa Water Reliability Facility
- Mesa Water District: Contact us
- U.S. Geological Survey: water hardness in the United States
- Irvine Ranch Water District 2026 Water Quality Report: about IRWD
- Irvine Ranch Water District 2026 Water Quality Report: water hardness
- U.S. Department of Energy: which water heater is right for you
- City of Costa Mesa plumbing permit application
- Angi: water heater installation cost
- Angi: tankless water heater cost
- City of Costa Mesa Housing Element, April 2021
- EPA WaterSense: Fix a Leak Week