Drinking Water Quality Data

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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.

Drinking Water Quality Data

Drinking Water Quality Data

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.

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. Community water systems and population served by average and maximum annual arsenic concentrations
  • Chart 1. Community water systems and population served by average and maximum annual arsenic concentrations
  • Table 2. Community water systems and population served by average quarterly arsenic concentrations
  • Chart 2. Community water systems and population served by average quarterly arsenic concentrations

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

Yearμg/LAverage Arsenic ConcentrationMaximum Arsenic Concentration
Number of CWSNumber of People ServedNumber of CWSNumber of People Served
1999Not reported2,2417,087,9072,2417,087,907
0 – <575232,981,01471831,975,776
5 – <1043215,70960380,132
10 – <202349,36530837,588
20 – <307212,6501454,707
30+47647211,299
2000Not reported1,9185,479,2321,9185,479,232
0 – <51,03034,446,0111,00233,549,238
5 – <1068317,73180931,105
10 – <203381,68439243,896
20 – <3011218,6541341,879
30+104,09718302,059
2001Not reported1,6194,526,5661,6194,526,566
0 – <51,27734,936,3451,24233,694,374
5 – <1097598,9331091,358,575
10 – <2046209,76061582,113
20 – <3014211,59516101,193
30+1764,21023284,588
2002Not reported1,3174,153,0731,3174,153,073
0 – <51,52835,192,6511,48834,006,360
5 – <10134743,7081431,479,237
10 – <2054184,40471359,413
20 – <3019213,35125275,491
30+1860,22226273,835
2003Not reported1,0843,423,9001,0843,423,900
0 – <51,71435,969,1251,67235,097,705
5 – <10156657,2701721,029,703
10 – <2068347,87286617,856
20 – <3026140,8332670,456
30+228,40930307,789
2004Not reported8792,587,3178792,587,317
0 – <51,89436,767,1051,82130,574,721
5 – <10156669,1231935,992,851
10 – <2084232,932103917,163
20 – <3036278,73839141,152
30+2112,19435334,205
2005Not reported7321,599,8307321,599,830
0 – <52,00937,467,7131,94635,612,268
5 – <10176870,8231991,773,511
10 – <2097327,698109855,844
20 – <3032270,02446359,012
30+2411,32138346,944
2006Not reported6441,511,8966441,511,896
0 – <52,08437,593,9742,02732,103,778
5 – <101821,076,2401975,627,122
10 – <2098276,424109690,652
20 – <303323,31947395,632
30+2965,55646218,329
2007Not reported5431,104,0505431,104,050
0 – <52,16537,851,1632,09032,078,514
5 – <101991,306,5392356,229,941
10 – <2096202,404101832,663
20 – <303562,09149103,054
30+3221,16252199,187
2008Not reported437698,939437698,939
0 – <52,24038,141,4682,14329,218,645
5 – <102201,288,2422508,661,689
10 – <20106335,1411291,592,495
20 – <303573,66153194,495
30+329,95858181,146

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

Not reported0 – <5μg/L5 – <10μg/L10 – <20μg/L20 – <30μg/L30+μg/L
YearQuarter# CWS# People# CWS# People# CWS# People# CWS# People# CWS# People# CWS# People
199912,95426,899,28810613,177,8054312,9363144,8711600211,909
22,94127,055,57911813,204,108460,045215,3304212,285162
32,96831,736,032898,241,0483321,636530,662373,1362144,895
42,99035,843,732694,509,790512,566324,5213156,80000
200012,96829,277,2268911,021,137688,66711,7851144,833513,761
22,93727,231,18511713,072,634376,09441,874420,4725145,150
32,96231,616,540998,659,545130,000484,507111,8473144,970
42,96030,734,107979,582,022212,8695162,877454,15821,376
200112,93928,198,38911412,013,842548,5628232,359153,5203737
22,92125,808,83513314,513,176516,83911204200,80067,639
32,94126,463,06311313,749,821330,717230,582365,9678207,259
42,94534,172,2321045,822,2085209,1538226,815361,070555,931
200212,91927,230,63212712,571,2769508,5747119,446361,595555,886
22,90125,737,58514714,425,008362,190656,9045209,522856,200
32,90026,265,48813913,870,6451068,067886,9157253,60162,693
42,91626,026,30412614,061,10110155,694634,6244210,800858,886
200312,91627,375,38312912,844,944522,0977180,061566,474858,450
22,88925,596,35514814,460,4541080,3139140,1767212,747757,364
32,91326,323,75712813,650,95110246,3038112,4305210,87563,093
42,89425,825,64813914,087,860788,68014419,7756119,463105,983
200412,89627,543,61213812,542,67212147,8279187,726767,646857,926
22,89323,946,33713215,973,65814356,3371325,19411231,653714,230
32,89126,191,95913513,744,49617230,3799115,38310208,144857,048
42,90426,470,51313213,609,43113223,701927,1235200,913715,728
200512,90625,631,97312414,001,52012430,01413195,5694175,22511113,108
22,90325,538,99713214,656,7381158,1411128,692361,02010203,821
32,90127,212,13811812,129,55121794,4219107,29911263,8641040,136
42,90628,005,28011511,923,84617309,57414189,245662,6001256,864
200612,90631,096,7261208,765,72412478,7311884,248412,13710109,843
22,88225,063,66113314,987,73914306,4671854,598876,1761558,768
32,88829,707,8831239,935,40616599,53523225,736762,5401316,309
42,88424,224,13411515,565,33920416,23127270,8101012,8721458,023
200712,84625,023,91315215,054,29221255,6692982,2197114,6651516,651
22,82123,426,76117216,398,02118493,71233127,6141398,232133,069
32,82924,653,54315314,878,50722705,91836199,7651040,9422068,734
42,81525,563,96216314,041,68733742,88034127,2681268,641132,971
200812,80125,740,08416614,091,73531490,94142136,2351385,109173,305
22,80623,717,75516615,838,52928440,26544451,2271798,38791,246
32,80723,940,42315515,682,05635705,97937145,5051569,252214,194
42,81224,905,93415914,869,96236580,33034107,2011582,107141,875

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.

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

Yearmg/L
Nitrate Nitrogen
Average Nitrate ConcentrationMaximum Nitrate Concentration
Number of CWSNumber of People ServedNumber of CWSNumber of People Served
1999Not reported1,9045,437,1901,9045,437,190
0 – <397331,076,67488824,334,673
3 – <51012,343,967951,121,481
5 – <10871,689,0931618,987,903
10+548522666,162
2000Not reported1,7975,039,7981,7975,039,798
0 – <31,08431,620,55897324,297,896
3 – <51102,338,2921356,325,040
5 – <10701,491,7991414,146,063
10+956,96224738,612
2001Not reported1,6294,707,6581,6294,707,658
0 – <31,19031,655,7281,06523,880,632
3 – <51492,510,3341561,589,190
5 – <10891,655,3151919,592,020
10+1318,37429777,909
2002Not reported1,3474,210,8321,3474,210,832
0 – <31,35531,267,1161,23122,998,645
3 – <51952,669,4391781,776,795
5 – <101602,398,63226810,540,879
10+131,390461,020,258
2003Not reported1,2013,160,5961,2013,160,596
0 – <31,46532,001,5971,31323,037,589
3 – <52133,070,4892116,505,067
5 – <101732,312,8412877,213,544
10+181,88658630,613
2004Not reported1,1323,131,5351,1323,131,535
0 – <31,52631,910,2971,35321,952,318
3 – <52172,966,5182156,243,459
5 – <101762,461,7283177,877,244
10+1977,331531,342,853
2005Not reported1,0842,675,2711,0842,675,271
0 – <31,56731,477,7761,38722,249,508
3 – <52313,947,5482296,356,698
5 – <101672,444,4812967,387,753
10+212,333741,878,179
2006Not reported1,0713,081,0821,0713,081,082
0 – <31,55830,823,4001,40425,980,746
3 – <52404,272,8282011,639,237
5 – <101782,350,8993237,800,872
10+2319,200712,045,472
2007Not reported9712,573,2929712,573,292
0 – <31,58730,716,1401,44921,577,095
3 – <52784,560,9932216,283,771
5 – <102102,677,3723357,529,136
10+2419,612942,584,115
2008Not reported9233,512,4479233,512,447
0 – <31,63130,750,1511,47220,715,962
3 – <52793,956,3512316,826,370
5 – <102112,308,3823577,140,147
10+2620,078872,352,483

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

Not reported0 – <3mg/L3 – <5mg/L5 – <10mg/L10+mg/L
YearQuarter# CWS# People# CWS# People# CWS# People# CWS# People# CWS# People
199912,71714,190,80324518,981,322625,875,173441,499,9312180
22,70914,253,15426123,018,278472,016,737491,258,7904450
32,82023,369,18915414,012,783421,547,799521,617,2482390
42,69113,989,37125618,612,709586,379,838621,562,73832,753
200012,71314,539,68725722,546,643441,899,103551,561,951125
22,70414,477,11227823,635,19331637,832541,797,0603212
32,69112,489,38027024,592,504532,071,636531,336,761357,128
42,77724,476,73817612,524,084531,756,846571,788,19671,545
200112,75623,665,67919613,690,608501,219,500621,971,1576465
22,65813,311,52628423,864,854571,649,485591,703,4651218,079
32,64111,557,44130525,689,919531,465,836601,816,1441118,069
42,63312,984,11228823,310,279792,446,063641,806,3156640
200212,61411,557,85628625,647,292861,858,967781,482,4596835
22,60010,897,15928725,348,354761,968,573992,332,31381,010
32,61711,084,50129425,018,671692,272,000822,154,788817,449
42,61311,325,71426224,835,8411002,815,514861,539,659930,681
200312,57910,439,17129025,260,607953,265,7571011,551,035530,839
22,55710,322,44933125,926,210702,023,8581052,257,309717,583
32,56511,010,80030924,587,925822,904,8461072,026,176717,662
42,55810,903,68429524,412,870932,905,9631142,323,855101,037
200412,57610,934,99731425,069,608752,644,766981,822,173775,865
22,55010,319,21732225,677,162932,586,002971,919,462845,566
32,55811,106,14229824,043,022993,088,5911042,278,1871131,467
42,56110,608,01229023,530,3901003,927,7541092,433,4411047,812
200512,55910,371,61827824,035,9961053,865,8761182,226,0621047,857
22,55210,375,50330524,587,207903,057,6051112,480,5261246,568
32,56610,162,44626424,307,3271123,325,2781132,733,8551518,503
42,54710,091,31930524,692,282963,596,1521062,148,8501618,806
200612,5439,944,95527924,175,3861344,162,6571032,246,6891117,722
22,5349,737,78430825,186,4881133,461,7621002,143,1201518,255
32,5268,971,88630025,399,5531123,672,5531162,484,3881619,029
42,5369,938,88929124,340,5281173,883,9331132,365,7621318,297
200712,4979,597,66529524,800,3421293,403,6551362,744,542131,205
22,51710,110,92127623,942,5651524,228,4951102,263,910151,518
32,5219,667,51528123,635,6011254,201,0101182,824,12825219,155
42,5269,998,92227124,226,8431303,241,1171323,079,161111,366
200812,5089,623,70231925,237,3261053,416,3941262,268,982121,005
22,5009,393,88728024,472,6081424,135,4251302,538,452187,037
32,5059,667,51230824,680,9361033,500,5631412,680,3161318,082
42,4979,674,00828224,813,7581233,372,9821492,666,7441919,917

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