Local and imported drinking water quality results
PHG (MCLG)
Average local treated
Average local treated
Average imported MWD
Range of detections
MCL violation? Typical source of contaminant
Chemical
MCL
Radiologicals — tested in 2025 Alpha Radiation (pCi/L)
15
0 0
1.2 0.6
ND ND
ND ND ND ND
ND -5 ND - 6
No No
Erosion of natural deposits
Beta Radiation (pCi/L) Radium-228 (pCi/L)
50
Decay of natural and man-made deposits
Not regulated
0.019
0.33 0.55
0.42 0.45
ND - 0.42
n/a
Erosion of natural deposits Erosion of natural deposits Erosion of natural deposits
Combined Radium-226 + 228 (pCi/L)
5
0
ND - 1.0
No No
Uranium (pCi/L)
20
0.43
1.8
1.9
1
ND - 3
Inorganic chemicals — tested in 2025 Aluminum (ppb)
1000
600
ND 1.8
ND 1.7
Highest RAA = 58 ppb
ND - 123 ND - 2.8 9.9 - 141 ND - 8.4
No No No No No No No No No No No No No No No No No No
Treatment process residue, natural deposits
Arsenic (ppb) Barium (ppb) Bromate (ppb) Chlorine (ppm)
10
0.004 2000
ND
Erosion of natural deposits Erosion of natural deposits
1000
23.1
129 NR 2.3
130
10
0.1 4.0
NR 2.6 0.1
Highest RAA = 2.4 ppb
Byproduct of drinking water ozonation
4.0
Highest RAA = 2.6 ppm 1.1 - 3.9
Drinking water disinfectant added for treatment Erosion of natural deposits; industrial discharge Erosion of natural deposits; IRWD does not add fluoride to its local treated groundwater and surface water
Hexavalent Chromium (ppb)
10
0.02
ND
ND NR 0.7 ND ND
ND - 0.2
Fluoride (ppm) naturally-occurring
2
1
0.32
0.33
0.05 - 0.81
Control range 0.6 - 1.2 ppm Optimal level 0.7 ppm
Fluoride (ppm) treatment-related
NR 1.9 2.0
NR ND ND
0.6 - 0.8 ND - 4.0 ND - 4.0
Water additive for dental health
Nitrate (ppm as N)
10 10
10 10
Fertilizers, septic tanks Fertilizers, septic tanks
Nitrate+Nitrite (ppm as N)
Secondary standards* — tested in 2025 Aluminum (ppb)
200* 500*
600
ND
ND
Highest RAA = 58 ppb
ND - 123 17.7 - 118
Treatment process residue, natural deposits Leaching from natural deposits; seawater influence
Chloride (ppm) Color (color units)
n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a
72.1
109
92
15*
3
<3
1
ND - 3 ND - 3
Naturally occurring organic substances Naturally occurring organic materials Ions in water; seawater influence Runoff or leaching from natural deposits Runoff or leaching from natural deposits
Odor (TON)
3*
1
1
ND
Specific Conductance (µmho/cm)
1,600*
561 103
1,049
873 182 545
363 - 1151 22.4 - 221 196 - 748
Sulfate (ppm)
500*
219 625
Total Dissolved Solids (ppm)
1,000*
343 0.10
Turbidity (NTU)
5*
Highest RAA = 0.25 NTU†
ND
ND - 7†
Erosion of natural deposits
Unregulated contaminants – tested in 2025 Alkalinity, Total (ppm as CaCO3) Not regulated
133 148 172
119 149 143
108
66 - 269 81 - 273 ND - 262 0.13 - 0.15 16.1 - 130 ND - 2.5
n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a
Runoff or leaching from natural deposits Runoff or leaching from natural deposits Runoff or leaching from natural deposits Runoff or leaching from natural deposits Runoff or leaching from natural deposits Runoff or leaching from natural deposits Byproduct of drinking water chlorination
Bicarbonate (ppm as HCO3)
Not regulated
NR
Boron (ppb)
NL = 1000
130
Bromide (ppm) Calcium (ppm) Carbonate (ppm) Chlorate (ppb)
Not regulated Not regulated Not regulated
0.14 48.5
NR
NR 56 NR
73
0.6 NR
<0.6
NL = 800
NR
32.0 12.4 0.58 236 13.8 22.0
32.0
Corrosivity (Aggressiveness)
Not regulated Not regulated Not regulated Not regulated Not regulated Not regulated
12.0 0.24 214 12.5 14.5
11.9
11.0 - 12.6
Elemental balance in water Elemental balance in water
Corrosivity (Langlier Index) @ Ambient Temp
(-0.66) - 0.61
0.07 293
Hardness, Total (ppm as CaCO3) Hardness, Total (grains/gal)
52.0 - 469 12.5 - 17.1 0.59 - 35.0
Runoff or leaching from natural deposits Runoff or leaching from natural deposits Runoff or leaching from natural deposits
17.1
Magnesium (ppm) Molybdenum (ppb)
26.9
9.6
5.2
NR
4.9 - 5.5
Drinking water treatment chemical for aesthetic quality Industrial chemical factory discharges; runoff/leaching from landfills; used in fire-retarding foams and various industrial processes Measures of the balance between pH and calcium carbonate saturation in the water
0.007 (0)
Perfluorooctanoic acid (PFOA) (ppt)
NL = 4.0
1.2
ND
ND
ND - 2.3
No
Calcium Carbonate Precipitation Potential (CCPP) (as CaCO3) (ppm)
Not regulated
n/a
NR
NR
7.4
2.4 - 11
n/a
pH (pH units)
Not regulated Not regulated Not regulated
n/a n/a n/a n/a n/a n/a
8.0
7.6 5.4 101 NR 2.9 ND
8.3 4.3 88
7.0 - 8.6 0.61 - 6.0 24.7 - 106 333 - 657
n/a n/a n/a
Acidity, hydrogen Ions
Potassium (ppm)
1.5
Runoff or leaching from natural deposits Runoff or leaching from natural deposits Runoff or leaching from natural deposits Various natural and man-made sources
Sodium (ppm)
61.2
Total Dissolved Solids, Calculated (TDS)
1000*
NR
507 2.4
No TT
Total Organic Carbon (ppm)
TT
0.20
ND - 2.9 ND - 11.1
Vanadium (ppb) Runoff or leaching from natural deposits Your water has been tested for many more chemicals than are listed above, including metals (such as mercury), pesticides and volatile organic compounds. Chemicals not detected in any water sources are not included in the table. ppb = parts-per-billion; ppm = parts-per-million; ppt = parts-per-trillion; pCi/L = picoCuries per liter; ntu = nephelometric turbidity units; ND = not detected; N/A = not applicable; NR = not required to be tested; < = average is less than the detection limit for reporting purposes; MCL = Maximum Contaminant Level; (MCLG) = federal MCL Goal; PHG = California Public Health Goal; µmho/cm = micromho per centimeter; NL = Notification Level; TT = Treatment Technique; RAA = Highest Running Annual Average; *Contaminant is regulated by a secondary standard to maintain aesthetic qualities (taste, odor, color). Turbidity — Combined Filter Effluent Treatment Technique TT violation? Typical source Baker Water Treatment Plant 1) Highest single turbidity measurement 0.03 NTU No Soil run-off 2) Percentage of samples less than or equal to 0.3 NTU 100% No Soil run-off Metropolitan Water District Diemer Filtration Plant 1) Highest single turbidity measurement 0.05 NTU No Soil run-off 2) Percentage of samples less than or equal to 0.3 NTU 100% No Soil run-off NL = 50 4.9 ND n/a Turbidity is the measurement of the cloudiness of water, an indication of particulate matter, some of which might include harmful microorganisms. Low turbidity in treated surface water is a good indicator of effective filtration. Filtration is called a treatment technique (TT) . TT is a required process intended to reduce the level of contaminants in drinking water that are difficult and sometimes impossible to measure directly. Data is taken from a continuous online meter. +On Jan. 21, 2025, a higher than normal (7 NTU) grab sample was reported. This value is inconsistent with the continuous online analyzer, which showed a reading of 0.0259 NTU at the same time that the grab sample was taken. The available evidence suggests that the higher than normal grab sample was not a valid representation of the water quality produced by the plant at the time. No other result above 0.1 NTU was reported throughout the year.
IRWD Water Quality Report 2026 | Page 11
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