California utilities with very hard water.

Above 180 mg/L (10.5 grains per gallon). 718 utilities serving 5.6 million people as they report it, largest first.

101 to 200 of 718, by people served

California utilities with very hard water, 101 to 200, 101 to 200
Utility	Based in	Serves	Hardness, mg/L	Grains per gallon
Peter Pitchess Honor Rancho Detn. Ctr	Castaic	7,000	320	18.7
Ojai Water System	Oak View	6,801	408	23.8
Nuevo Water Company	Nuevo	6,733	440	25.7
Santa Ana River Water Company	Jurupa Valley	6,475	300	17.5
City of Holtville	Holtville	6,355	330	19.3
Hidden Valley Lake CSD	Hidden Valley Lake	6,235	231	13.5
City of Industry Waterworks Systems	La Puente	6,151	346	20.2
City of Gustine	Gustine	6,138	360	21.1
Ventura River Water District	Ojai	6,100	399	23.3
Cambria Comm Services Dist	Cambria	6,038	311	18.2
Solvang Water Division	Solvang	5,980	592	34.6
Glen Helen Water System	San Bernardino	5,900	260	15.2
La Habra Heights CWD	La Habra Heights	5,682	319	18.6
Serrano Water District	Villa Park	5,659	340	19.9
City of Williams	Williams	5,538	221	12.9
Pleasant Valley Mutual Water Co	Camarillo	5,306	690	40.3
City of Buellton Water Division	Buellton	5,091	510	29.8
City of Needles	Needles	4,872	335	19.6
La Cumbre Mutual Water Co	Santa Barbara	4,861	490	28.7
Los Angeles Cwwd 37 - Acton	Alhambra	4,782	305	17.8
Mojave PUD	Mojave	4,699	255	14.9
Valley View Mutual Water Co.	Baldwin Park	4,613	208	12.2
Suburban Water Systems - Sativa	Covina	4,372	248	14.5
Correctional Training Facility - Soledad	Soledad	4,357	275	16.1
Meiners Oaks CWD	Ojai	4,200	490	28.7
Golden State Water Co - Wrightwood	Apple Valley	4,153	460	26.9
Centinela State Prison	Imperial	4,100	335	19.6
Farm Mutual W.C. (The)	Wildomar	4,026	440	25.7
Maywood Mutual Water Co. #1	Huntington Park	3,851	227	13.3
Mission Hills CSD	Lompoc	3,600	276	16.2
Naval Base Ventura County, Port Hueneme	Point Mugu	3,500	421	24.6
Presidio of San Francisco	San Francisco	3,500	235	13.7
Psmcsd - Pajaro	Royal Oaks	3,500	277	16.2
East Orange County WD - Rz	Orange	3,464	323	18.9
Box Springs Mutual WC	Moreno Valley	3,382	320	18.7
Arbuckle Public Utility District	Arbuckle	3,251	222	13
Amarillo Mutual Water Company	Rosemead	3,134	240	14
San Miguel Community Services District	San Miguel	3,019	358	20.9
Cci - Tehachapi	Tehachapi	2,993	265	15.5
O'Connor Tract Co - Operative Water Co.	Palo Alto	2,789	245	14.3
Town of Yountville	Yountville	2,785	212	12.4
Central Water District	Aptos	2,726	230	13.5
Frazier Park PUD	Frazier Park	2,592	451	26.4
Cayucos Beach Mutual Water Company	Cayucos	2,567	430	25.1
Terrace Water Company	Colton	2,400	280	16.4
City of San Juan Bautista	San Juan Bautista	2,335	382	22.3
Little Bear Water Company	Soledad	2,327	221	12.9
Las Flores Water Co.	Altadena	2,211	310	18.1
City of Westmorland	Westmorland	2,202	340	19.9
Mil Potrero MWC	Pine Mountain Club	2,200	410	24
Morro Rock Mutual Water Co	Cayucos	2,181	377	22
Cwsc Las Lomas	San Jose	2,132	257	15
Crestview Mutual Water Co	Camarillo	2,079	402	23.5
Cal American Water Company - Piru	Rosemead	2,023	658	38.5
Eastside Water Association	Midway City	2,000	181	10.6
Golden State Water Company - Tanglewood	Santa Maria	1,979	405	23.7
Vineyard Avenue Acres MWC	Oxnard	1,820	550	32.2
Seeley CWD	Seeley	1,729	330	19.3
Golden State Water Co - Morongo del Sur	Apple Valley	1,715	270	15.8
Cal American WC - Rio Plaza	Rosemead	1,712	554	32.4
San Miguelito MWC	Avila Beach	1,600	550	32.2
Devore WC	Devore	1,574	260	15.2
Lynwood Park Mutual Water Co.	Compton	1,564	274	16
Los Alamos Community Services District	Los Alamos	1,534	249	14.6
Lake County CSA 2 - Spring Valley	Lakeport	1,531	218	12.8
Cal Am Water Company - Hidden Hills	Pacific Grove	1,521	313	18.3
White Fence Farms MWC No. 1	Palmdale	1,518	310	18.1
Golden State Water Company - Edna	Santa Maria	1,495	430	25.1
Cal Am Water Company - Toro	Pacific Grove	1,442	222	13
Ventura Cwwd No. 19 - Somis	Moorpark	1,429	298	17.4
Lebec County Water District	Lebec	1,379	370	21.6
Garden Acres Mutual Water Co	Oxnard	1,335	569	33.2
Gateway	El Centro	1,215	330	19.3
Vineyard Ave Estates MWC	Oxnard	1,200	453	26.5
Maxwell Public Utility District	Maxwell	1,175	215	12.5
Fairoaks PWS #44	Stockton	1,172	268	15.7
Atascadero State Hospital	Atascadero	1,100	435	25.5
Slo CSA No. 16 - Shandon	San Luis Obispo	1,085	275	16.1
Cal Am - West San Martin	Pacific Grove	1,079	243	14.2
Los Angeles Cwwd 40, Reg. 39 - Rock Creek	Alhambra	1,030	285	16.7
Cws Southlake System	San Jose	1,015	252	14.7
Dempsey Road Mutual Water Co	Oxnard	990	272	15.9
Apple Valley Heights CWD	Apple Valley	983	263	15.4
Rio Manor Mutual Water Co	Camarillo	983	551	32.2
Nyeland Acres Mutual Water Co	Oxnard	975	464	27.1
City of Modesto - Grayson	Modesto	917	778	45.5
Rancho Pauma Mutual WC	Pauma Valley	899	355	20.8
South Midway City Mutual Water Co.	Midway City	891	257	15
Hillsview Homes	Modesto	887	655	38.3
Plantation on the Lake Park	Calimesa	885	200	11.7
Psmcsd - Sunny Mesa	Royal Oaks	880	221	12.9
Lake of the Woods MWC	Frazier Park	875	390	22.8
Descanso Community Water District	Sacramento	870	200	11.7
Cuesta la Honda Guild Inc	La Honda	863	360	21.1
San Joaquin County - Wilkinson Manor	Stockton	851	250	14.6
Los Prietos Complex	Solvang	845	688	40.2
Loleta C.S.D.	Loleta	828	310	18.1
Senior Canyon Mutual Water Co	Ojai	800	409	23.9
Daggett Comm Svcs Dist	Daggett	795	495	28.9
Mountain Mesa WC	Bakersfield	777	335	19.6

Source: California State Water Resources Control Board, Division of Drinking Water, 2,449 utilities, results from Jan. 2, 2019 to July 14, 2026, read Oct. 10, 2026. Each sampling point is taken at its median; a figure is typical where every point falls in one band.

Also: 7 utilities’ own water quality reports, read by hand, each named on the utility’s page.

Bands are the U.S. Geological Survey’s, at 17.1 mg/L to the grain. People served is what each utility reports; where one sells water to another, the same people can be counted twice. How hardness is measured here.

101 to 200 of 718, by people served

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