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California Environmental Health Tracking Program

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Last Edited: 4/12/2011

Drinking Water Quality Data

Please select from the following indicator areas or scroll down:

Challenges in using the water quality data for public health:

The data that we used to create these tables were originally collected for regulatory compliance purposes. Because of this, there are many limitations to using this information for public health purposes. Translating the results into meaningful estimates of potential exposure to water contaminants is difficult.

This is particularly true for water systems that have multiple sources of water. When these sources are independently added to the distribution system, areas of the water system can have different water quality for which the data on this page do not take into account. Water systems with this type of configuration tend to be large in size and population.

Moreover, results tend toward overestimating the number of people exposed to a contaminant. Community Water Systems (CWS) are required to estimate the number of people served for regulatory purposes. Because of the complexity of water systems, there is no way to know exactly how many people each water system serves, and the methods for estimation are inaccurate. Calculations show that the overall estimate for the population served by CWS in the state is more than 3 million people greater than expected based on the California population. While the estimates are entirely appropriate for regulatory purposes, those examining the data for public health purposes must be aware of this limitation.

You are encouraged to peruse the metadata to learn the technical details of how the raw data were processed to result in the measures on this page.


Why our data may look different from other reports:

The California Office of Drinking Water (ODW) and the US EPA also report on drinking water quality. The data presented here may not exactly match what is found in the ODW and EPA reports for a number of reasons, including:

  • We summarized the information in a slightly different way. For example, ODW reports on all public water systems whereas we are focusing on a subset of those systems (the Community Water Systems)
  • We used data from different points in time

 

Looking toward the future

The California Environmental Health Tracking Program (CEHTP) is working with a variety of partners to enhance existing water quality data to facilitate public health surveillance. Currently, the CEHTP is developing a web-based mapping application that allows water system personnel to collaboratively contribute to the first-ever statewide water system service area map. Having this geographic data will allow us to better estimate population served and to drill-down to more spatially-refined water system units.

 

Download data

 


Public Water Use

The number of people receiving water from active community water systems (CWS) as reported to the State under the Safe Drinking Water Act as of May, 2010 is 40,547,409. Please see the Monitoring and Regulation section for more information on how the number of people served by CWS is determined. Please see the Measures and Limitations section for discussion on why this figure is inaccurate.

 


Arsenic Levels in Drinking Water

Table 1. Number of people served and number of community water systems by mean and and maximum annual arsenic concentrations, 1999-2008

Year μg/L Average Arsenic Concentration Maximum Arsenic Concentration
Number of CWS Number of People Served Number of CWS Number of People Served
1999 Not reported 2,241 7,087,907 2,241 7,087,907
0 - <5 752 32,981,014 718 31,975,776
5 - <10 43 215,709 60 380,132
10 - <20 23 49,365 30 837,588
20 - <30 7 212,650 14 54,707
30+ 4 764 7 211,299
2000 Not reported 1,918 5,479,232 1,918 5,479,232
0 - <5 1,030 34,446,011 1,002 33,549,238
5 - <10 68 317,731 80 931,105
10 - <20 33 81,684 39 243,896
20 - <30 11 218,654 13 41,879
30+ 10 4,097 18 302,059
2001 Not reported 1,619 4,526,566 1,619 4,526,566
0 - <5 1,277 34,936,345 1,242 33,694,374
5 - <10 97 598,933 109 1,358,575
10 - <20 46 209,760 61 582,113
20 - <30 14 211,595 16 101,193
30+ 17 64,210 23 284,588
2002 Not reported 1,317 4,153,073 1,317 4,153,073
0 - <5 1,528 35,192,651 1,488 34,006,360
5 - <10 134 743,708 143 1,479,237
10 - <20 54 184,404 71 359,413
20 - <30 19 213,351 25 275,491
30+ 18 60,222 26 273,835
2003 Not reported 1,084 3,423,900 1,084 3,423,900
0 - <5 1,714 35,969,125 1,672 35,097,705
5 - <10 156 657,270 172 1,029,703
10 - <20 68 347,872 86 617,856
20 - <30 26 140,833 26 70,456
30+ 22 8,409 30 307,789
2004 Not reported 879 2,587,317 879 2,587,317
0 - <5 1,894 36,767,105 1,821 30,574,721
5 - <10 156 669,123 193 5,992,851
10 - <20 84 232,932 103 917,163
20 - <30 36 278,738 39 141,152
30+ 21 12,194 35 334,205
2005 Not reported 732 1,599,830 732 1,599,830
0 - <5 2,009 37,467,713 1,946 35,612,268
5 - <10 176 870,823 199 1,773,511
10 - <20 97 327,698 109 855,844
20 - <30 32 270,024 46 359,012
30+ 24 11,321 38 346,944
2006 Not reported 644 1,511,896 644 1,511,896
0 - <5 2,084 37,593,974 2,027 32,103,778
5 - <10 182 1,076,240 197 5,627,122
10 - <20 98 276,424 109 690,652
20 - <30 33 23,319 47 395,632
30+ 29 65,556 46 218,329
2007 Not reported 543 1,104,050 543 1,104,050
0 - <5 2,165 37,851,163 2,090 32,078,514
5 - <10 199 1,306,539 235 6,229,941
10 - <20 96 202,404 101 832,663
20 - <30 35 62,091 49 103,054
30+ 32 21,162 52 199,187
2008 Not reported 437 698,939 437 698,939
0 - <5 2,240 38,141,468 2,143 29,218,645
5 - <10 220 1,288,242 250 8,661,689
10 - <20 106 335,141 129 1,592,495
20 - <30 35 73,661 53 194,495
30+ 32 9,958 58 181,146

 

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Chart 1. Number of by arsenic concentrations, 1999-2008

 

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Table 2. Community water systems and population served by average quarterly arsenic concentrations, 1999-2008

  Not reported 0 - <5μg/L 5 - <10μg/L 10 - <20μg/L 20 - <30μg/L 30+μg/L
Year Quarter # CWS # People # CWS # People # CWS # People # CWS # People # CWS # People # CWS # People
1999 1 2,954 26,899,288 106 13,177,805 4 312,936 3 144,871 1 600 2 11,909
2 2,941 27,055,579 118 13,204,108 4 60,045 2 15,330 4 212,285 1 62
3 2,968 31,736,032 89 8,241,048 3 321,636 5 30,662 3 73,136 2 144,895
4 2,990 35,843,732 69 4,509,790 5 12,566 3 24,521 3 156,800 0 0
2000 1 2,968 29,277,226 89 11,021,137 6 88,667 1 1,785 1 144,833 5 13,761
2 2,937 27,231,185 117 13,072,634 3 76,094 4 1,874 4 20,472 5 145,150
3 2,962 31,616,540 99 8,659,545 1 30,000 4 84,507 1 11,847 3 144,970
4 2,960 30,734,107 97 9,582,022 2 12,869 5 162,877 4 54,158 2 1,376
2001 1 2,939 28,198,389 114 12,013,842 5 48,562 8 232,359 1 53,520 3 737
2 2,921 25,808,835 133 14,513,176 5 16,839 1 120 4 200,800 6 7,639
3 2,941 26,463,063 113 13,749,821 3 30,717 2 30,582 3 65,967 8 207,259
4 2,945 34,172,232 104 5,822,208 5 209,153 8 226,815 3 61,070 5 55,931
2002 1 2,919 27,230,632 127 12,571,276 9 508,574 7 119,446 3 61,595 5 55,886
2 2,901 25,737,585 147 14,425,008 3 62,190 6 56,904 5 209,522 8 56,200
3 2,900 26,265,488 139 13,870,645 10 68,067 8 86,915 7 253,601 6 2,693
4 2,916 26,026,304 126 14,061,101 10 155,694 6 34,624 4 210,800 8 58,886
2003 1 2,916 27,375,383 129 12,844,944 5 22,097 7 180,061 5 66,474 8 58,450
2 2,889 25,596,355 148 14,460,454 10 80,313 9 140,176 7 212,747 7 57,364
3 2,913 26,323,757 128 13,650,951 10 246,303 8 112,430 5 210,875 6 3,093
4 2,894 25,825,648 139 14,087,860 7 88,680 14 419,775 6 119,463 10 5,983
2004 1 2,896 27,543,612 138 12,542,672 12 147,827 9 187,726 7 67,646 8 57,926
2 2,893 23,946,337 132 15,973,658 14 356,337 13 25,194 11 231,653 7 14,230
3 2,891 26,191,959 135 13,744,496 17 230,379 9 115,383 10 208,144 8 57,048
4 2,904 26,470,513 132 13,609,431 13 223,701 9 27,123 5 200,913 7 15,728
2005 1 2,906 25,631,973 124 14,001,520 12 430,014 13 195,569 4 175,225 11 113,108
2 2,903 25,538,997 132 14,656,738 11 58,141 11 28,692 3 61,020 10 203,821
3 2,901 27,212,138 118 12,129,551 21 794,421 9 107,299 11 263,864 10 40,136
4 2,906 28,005,280 115 11,923,846 17 309,574 14 189,245 6 62,600 12 56,864
2006 1 2,906 31,096,726 120 8,765,724 12 478,731 18 84,248 4 12,137 10 109,843
2 2,882 25,063,661 133 14,987,739 14 306,467 18 54,598 8 76,176 15 58,768
3 2,888 29,707,883 123 9,935,406 16 599,535 23 225,736 7 62,540 13 16,309
4 2,884 24,224,134 115 15,565,339 20 416,231 27 270,810 10 12,872 14 58,023
2007 1 2,846 25,023,913 152 15,054,292 21 255,669 29 82,219 7 114,665 15 16,651
2 2,821 23,426,761 172 16,398,021 18 493,712 33 127,614 13 98,232 13 3,069
3 2,829 24,653,543 153 14,878,507 22 705,918 36 199,765 10 40,942 20 68,734
4 2,815 25,563,962 163 14,041,687 33 742,880 34 127,268 12 68,641 13 2,971
2008 1 2,801 25,740,084 166 14,091,735 31 490,941 42 136,235 13 85,109 17 3,305
2 2,806 23,717,755 166 15,838,529 28 440,265 44 451,227 17 98,387 9 1,246
3 2,807 23,940,423 155 15,682,056 35 705,979 37 145,505 15 69,252 21 4,194
4 2,812 24,905,934 159 14,869,962 36 580,330 34 107,201 15 82,107 14 1,875

 

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Chart 2. Number of by quarterly arsenic concentrations, 1999-2008

 

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Disinfection By-Products (DBP) Levels in Drinking Water

Sampling results related to Disinfection By-Products within distribution systems according to the Surface Water Treatment Rule are missing, because regional districts and labs for the most part are not currently reporting electronic distribution system sampling information to the Office of Drinking Water. The Office of Drinking Water expects to capture DBP data centrally and electronically with the migration of their systems to the EPA Safe Drinking Water Information System (SDWIS). A date for this migration has not been communicated to the California Environmental Health Tracking Program.

Previously, this page showed DBP violations data. Violations data are no longer being tracked by the Environmental Public Health Tracking Network.

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Nitrate Levels in Drinking Water

Table 3. Number of people served and number of community water systems by mean and and maximum annual nitrate concentrations, 1999-2008

Year mg/L
Nitrate Nitrogen
Average Nitrate Concentration Maximum Nitrate Concentration
Number of CWS Number of People Served Number of CWS Number of People Served
1999 Not reported 1,904 5,437,190 1,904 5,437,190
0 - <3 973 31,076,674 888 24,334,673
3 - <5 101 2,343,967 95 1,121,481
5 - <10 87 1,689,093 161 8,987,903
10+ 5 485 22 666,162
2000 Not reported 1,797 5,039,798 1,797 5,039,798
0 - <3 1,084 31,620,558 973 24,297,896
3 - <5 110 2,338,292 135 6,325,040
5 - <10 70 1,491,799 141 4,146,063
10+ 9 56,962 24 738,612
2001 Not reported 1,629 4,707,658 1,629 4,707,658
0 - <3 1,190 31,655,728 1,065 23,880,632
3 - <5 149 2,510,334 156 1,589,190
5 - <10 89 1,655,315 191 9,592,020
10+ 13 18,374 29 777,909
2002 Not reported 1,347 4,210,832 1,347 4,210,832
0 - <3 1,355 31,267,116 1,231 22,998,645
3 - <5 195 2,669,439 178 1,776,795
5 - <10 160 2,398,632 268 10,540,879
10+ 13 1,390 46 1,020,258
2003 Not reported 1,201 3,160,596 1,201 3,160,596
0 - <3 1,465 32,001,597 1,313 23,037,589
3 - <5 213 3,070,489 211 6,505,067
5 - <10 173 2,312,841 287 7,213,544
10+ 18 1,886 58 630,613
2004 Not reported 1,132 3,131,535 1,132 3,131,535
0 - <3 1,526 31,910,297 1,353 21,952,318
3 - <5 217 2,966,518 215 6,243,459
5 - <10 176 2,461,728 317 7,877,244
10+ 19 77,331 53 1,342,853
2005 Not reported 1,084 2,675,271 1,084 2,675,271
0 - <3 1,567 31,477,776 1,387 22,249,508
3 - <5 231 3,947,548 229 6,356,698
5 - <10 167 2,444,481 296 7,387,753
10+ 21 2,333 74 1,878,179
2006 Not reported 1,071 3,081,082 1,071 3,081,082
0 - <3 1,558 30,823,400 1,404 25,980,746
3 - <5 240 4,272,828 201 1,639,237
5 - <10 178 2,350,899 323 7,800,872
10+ 23 19,200 71 2,045,472
2007 Not reported 971 2,573,292 971 2,573,292
0 - <3 1,587 30,716,140 1,449 21,577,095
3 - <5 278 4,560,993 221 6,283,771
5 - <10 210 2,677,372 335 7,529,136
10+ 24 19,612 94 2,584,115
2008 Not reported 923 3,512,447 923 3,512,447
0 - <3 1,631 30,750,151 1,472 20,715,962
3 - <5 279 3,956,351 231 6,826,370
5 - <10 211 2,308,382 357 7,140,147
10+ 26 20,078 87 2,352,483

 

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Chart 3. Number of by nitrate concentrations, 1999-2008

 

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Table 4. Community water systems and population served by average quarterly nitrate concentrations, 1999-2008

  Not reported 0 - <3mg/L 3 - <5mg/L 5 - <10mg/L 10+mg/L
Year Quarter # CWS # People # CWS # People # CWS # People # CWS # People # CWS # People
1999 1 2,717 14,190,803 245 18,981,322 62 5,875,173 44 1,499,931 2 180
2 2,709 14,253,154 261 23,018,278 47 2,016,737 49 1,258,790 4 450
3 2,820 23,369,189 154 14,012,783 42 1,547,799 52 1,617,248 2 390
4 2,691 13,989,371 256 18,612,709 58 6,379,838 62 1,562,738 3 2,753
2000 1 2,713 14,539,687 257 22,546,643 44 1,899,103 55 1,561,951 1 25
2 2,704 14,477,112 278 23,635,193 31 637,832 54 1,797,060 3 212
3 2,691 12,489,380 270 24,592,504 53 2,071,636 53 1,336,761 3 57,128
4 2,777 24,476,738 176 12,524,084 53 1,756,846 57 1,788,196 7 1,545
2001 1 2,756 23,665,679 196 13,690,608 50 1,219,500 62 1,971,157 6 465
2 2,658 13,311,526 284 23,864,854 57 1,649,485 59 1,703,465 12 18,079
3 2,641 11,557,441 305 25,689,919 53 1,465,836 60 1,816,144 11 18,069
4 2,633 12,984,112 288 23,310,279 79 2,446,063 64 1,806,315 6 640
2002 1 2,614 11,557,856 286 25,647,292 86 1,858,967 78 1,482,459 6 835
2 2,600 10,897,159 287 25,348,354 76 1,968,573 99 2,332,313 8 1,010
3 2,617 11,084,501 294 25,018,671 69 2,272,000 82 2,154,788 8 17,449
4 2,613 11,325,714 262 24,835,841 100 2,815,514 86 1,539,659 9 30,681
2003 1 2,579 10,439,171 290 25,260,607 95 3,265,757 101 1,551,035 5 30,839
2 2,557 10,322,449 331 25,926,210 70 2,023,858 105 2,257,309 7 17,583
3 2,565 11,010,800 309 24,587,925 82 2,904,846 107 2,026,176 7 17,662
4 2,558 10,903,684 295 24,412,870 93 2,905,963 114 2,323,855 10 1,037
2004 1 2,576 10,934,997 314 25,069,608 75 2,644,766 98 1,822,173 7 75,865
2 2,550 10,319,217 322 25,677,162 93 2,586,002 97 1,919,462 8 45,566
3 2,558 11,106,142 298 24,043,022 99 3,088,591 104 2,278,187 11 31,467
4 2,561 10,608,012 290 23,530,390 100 3,927,754 109 2,433,441 10 47,812
2005 1 2,559 10,371,618 278 24,035,996 105 3,865,876 118 2,226,062 10 47,857
2 2,552 10,375,503 305 24,587,207 90 3,057,605 111 2,480,526 12 46,568
3 2,566 10,162,446 264 24,307,327 112 3,325,278 113 2,733,855 15 18,503
4 2,547 10,091,319 305 24,692,282 96 3,596,152 106 2,148,850 16 18,806
2006 1 2,543 9,944,955 279 24,175,386 134 4,162,657 103 2,246,689 11 17,722
2 2,534 9,737,784 308 25,186,488 113 3,461,762 100 2,143,120 15 18,255
3 2,526 8,971,886 300 25,399,553 112 3,672,553 116 2,484,388 16 19,029
4 2,536 9,938,889 291 24,340,528 117 3,883,933 113 2,365,762 13 18,297
2007 1 2,497 9,597,665 295 24,800,342 129 3,403,655 136 2,744,542 13 1,205
2 2,517 10,110,921 276 23,942,565 152 4,228,495 110 2,263,910 15 1,518
3 2,521 9,667,515 281 23,635,601 125 4,201,010 118 2,824,128 25 219,155
4 2,526 9,998,922 271 24,226,843 130 3,241,117 132 3,079,161 11 1,366
2008 1 2,508 9,623,702 319 25,237,326 105 3,416,394 126 2,268,982 12 1,005
2 2,500 9,393,887 280 24,472,608 142 4,135,425 130 2,538,452 18 7,037
3 2,505 9,667,512 308 24,680,936 103 3,500,563 141 2,680,316 13 18,082
4 2,497 9,674,008 282 24,813,758 123 3,372,982 149 2,666,744 19 19,917

 

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Chart 4. Number of by nitrate concentrations, 1999-2008

 

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