Potential Contaminants

Every year, Hawaii Water’s Water Quality Lab performs thousands of tests to monitor the quality of our water. If any contaminants are found, they are listed in the annual water quality report. However, most of the contaminants we test for are not found, so they are not listed in the water quality report.

The below table lists all of the contaminants that the Hawaii Department of Public Health (HDPH) requires Hawaii Water to test for, along with their maximum containment level (MCL). If you have any questions about this table or about the quality of your water, please contact the Hawaii Water Customer Center.

**Get more information on EPA’s adoption of MCLs for certain PFAS. No Hawaii Water drinking water sources are currently impacted by the new regulation.**

Contaminants Regulated by the Safe Drinking Water Branch (effective 3/4/09)


Total Coliform Bacteria:

  • 40 or more samples per month:
    No more than 5.0% of the samples may be total coliform positive
  • Less than 40 samples/month:
    No more than 1 sample/month may be total coliform positive

Fecal Coliform or E. coli Bacteria:

An acute violation occurs when:

  • A total coliform positive routine is followed by a fecal coliform or E. coli positive repeat, OR
  • A fecal coliform or E. coli positive routine is followed by a total coliform positive repeat
Inorganic Chemicals
Contaminant MCL (mg/l)
Arsenic 0.01
Asbestos 7 million fibers per liter
Barium 2.
Cadmium 0.005
Chromium 0.1
Copper (Action Level) 1.3
Lead (Action Level) 0.015
Mercury 0.002
Nitrate (as Nitrogen) 10.
Nitrite (as Nitrogen) 1.
Total Nitrate & Nitrite (as Nitrogen) 10.
Selenium 0.05
Fluoride 4.0
Antimony 0.006
Beryllium 0.004
Cyanide (as free Cyanide) 0.2
Thallium 0.002
Disinfection Byproducts
Contaminant MCL (mg/l)
(only Subpart H & P systems with population >10,000 until 1/1/04)
Total trihalomethanes
(sum of chloroform, bromoform, bromodichloromethane, dibromochloromethane)
Total Haloacetic Acids
(sum of mono-, di-, trichloroacetic acids and mono- and dibromoacetic acids.
Chlorite (usually formed under ClO2 use) 1.0
Bromate (brominated waters using ozone) 0.010
Contaminant MCL (mg/l)
(applies to all community water systems)
Gross alpha particle 15 pCi/l
Combined radium 226/228 5 pCi/l
Uranium 30 µg/l
Beta/photon emitters 4 mrem/yr (applies only to systems using surface water with populations > 100,000)
Organic Chemicals
Contaminant MCL (mg/l) Contaminant MCL (mg/l)
Volatile Organic Chemicals
Benzene 0.005 Styrene 0.1
Carbon Tetrachloride 0.005 Tetrachloroethylene 0.005
Chlorobenzene 0.1 Toluene 1.
o-Dichlorobenzene 0.6 1,1,1-Trichloroethane 0.2
para-Dichlorobenzene 0.075 Trichloroethylene 0.005
1,2-Dichloroethane 0.005 TCP (1,2,3-Trichloropropane) 0.0006
1,1-Dichloroethylene 0.007 Vinyl Chloride 0.002
cis-1,2-Dichloroethylene 0.07 Xylenes (total) 10.
trans-1,2-Dichloroethylene 0.1 Dichloromethane 0.005
DCP (1,2-Dichloropropane) 0.005 1,2,4-Trichlorobenzene 0.07
Ethylbenzene 0.7 1,1,2-Trichloroethane 0.005
Synthetic Organic Chemicals
Contaminant MCL (mg/l) Contaminant MCL (mg/l)
Alachlor 0.002 Dalapon 0.2
Atrazine 0.003 Di(2-ethylhexyl) adipate 0.4
Carbofuran 0.04 Di(2-ethylhexyl) phthalate 0.006
Chlordane 0.002 Dinoseb 0.007
DBCP (Dibromochloropropane) 0.00004 Diquat 0.02
2,4-D 0.07 Endothall 0.1
EDB (Ethylene Dibromide) 0.00004 Endrin 0.002
Heptachlor 0.0004 Glyphosate 0.7
Heptachlor Epoxide 0.0002 Hexachlorobenzene 0.001
Lindane 0.0002 Hexachlorocyclopentadiene 0.05
Methoxychlor 0.04 Oxamyl (Vydate) 0.2
Pentachlorophenol 0.001 Picloram 0.5
Toxaphene 0.003 Simazine 0.004
2,4,5-TP (Silvex) 0.05 2,3,7,8-TCDD (Dioxin) 3 X 10 -8
Benzo(a)pyrene 0.0002