Chlorate Contamination

Chlorate in Louisiana Drinking Water

Ranked by max chlorate detected (µg/L) · UCMR 3 data (2013–2015) · Data from EPA SDWIS & UCMR

Cities Tested

Over HA

67%

% Over HA

426.6 µg/L

State Avg

▲ 8% vs national

vs National

303

Health Violations

Analysis

Chlorate in Louisiana: what the data shows

Louisiana has 33 cities with chlorate data from the EPA's UCMR 3 program (2013–2015). Chlorate exceeded the 210 µg/L EPA lifetime health advisory in 22 of those cities. The state average max detected level is 426.6 µg/L. Chlorate is a disinfection byproduct that forms when chlorine dioxide or hypochlorite solutions are used to disinfect drinking water. It is most common in systems that use chlorine dioxide for taste-and-odor control or that store hypochlorite for extended periods. There is no federal MCL — the EPA lifetime health advisory is 210 µg/L. Chlorate can interfere with thyroid function by blocking iodide uptake, an effect of particular concern for pregnant women, infants, and people with thyroid conditions. Reverse osmosis and ion exchange (anion-specific) are effective at removing chlorate; standard activated carbon filters provide only modest reduction.

Comparison

Cities exceeding 210 µg/L EPA lifetime HA (no MCL)

Louisiana

67%

22 of 33 cities

→ ▲ 8% above national rate (worse)

National avg

59%

1866 of 3166 cities

City Map

Chlorate data across Louisiana

Each dot is a city with UCMR 3 chlorate testing data. Cities where chlorate exceeds the 210 µg/L EPA lifetime health advisory are highlighted. Size reflects population served.

Worst Offenders

Top 10 cities by chlorate level in Louisiana

Highest Chlorate levels (µg/L)

All Cities

All Louisiana cities ranked by chlorate level

#	City	Level	Over HA?	Violations	Grade
1	Houma	1900.0 µg/L	Over HA	6	B+
2	New Orleans	1100.0 µg/L	Over HA	27	F
3	Luling	1060.0 µg/L	Over HA	2	A-
4	Shreveport	1000.0 µg/L	Over HA	69	F
5	Mandeville	826.0 µg/L	Over HA	170	F
6	Belle Chasse	690.0 µg/L	Over HA	112	F
7	Barksdale Afb	630.0 µg/L	Over HA	16	A
8	Lafayette	610.0 µg/L	Over HA	42	F
9	Donaldsonville	601.0 µg/L	Over HA	69	C
10	Tioga	521.0 µg/L	Over HA	7	A-
11	Covington	517.0 µg/L	Over HA	93	F
12	Napoleonville	500.0 µg/L	Over HA	27	A-
13	Lockport	480.0 µg/L	Over HA	4	A+
14	Prairieville	470.0 µg/L	Over HA	30	F
15	Laplace	454.0 µg/L	Over HA	89	D+
16	Thibodaux	446.0 µg/L	Over HA	27	A-
17	Morgan City	400.0 µg/L	Over HA	20	B
18	St Joseph	370.0 µg/L	Over HA	56	F
19	Ringgold	300.0 µg/L	Over HA	68	F
20	Blanchard	254.0 µg/L	Over HA	26	B+
21	Pineville	240.0 µg/L	Over HA	15	F
22	Natchitoches	235.0 µg/L	Over HA	20	A
23	Lake Charles	100.0 µg/L	No	63	F
24	Monroe	70.0 µg/L	No	64	F
25	Baton Rouge	55.6 µg/L	No	30	F
26	Benton	40.0 µg/L	No	43	F
27	Plaquemine	38.6 µg/L	No	26	C-
28	Gretna	36.7 µg/L	No	19	A-
29	Sulphur	36.0 µg/L	No	24	B+
30	Lutcher	28.5 µg/L	No	20	B+
31	Jefferson	27.0 µg/L	No	2	A-
32	Chalmette	21.4 µg/L	No	23	A-
33	Arnaudville	20.1 µg/L	No	44	C

FAQ

Frequently asked questions about chlorate in Louisiana

Is chlorate in Louisiana tap water dangerous?

Chlorate has no federal MCL. The EPA lifetime health advisory is 210 µg/L. 22 cities in Louisiana exceed this level. Chlorate can interfere with thyroid iodide uptake, which is a particular concern for infants, pregnant women, and people with hypothyroidism.

Where does chlorate in Louisiana water come from?

Chlorate is a byproduct of chlorine-based disinfectants — particularly chlorine dioxide and hypochlorite (bleach) solutions. Levels tend to be higher in systems that use chlorine dioxide for taste-and-odor treatment or store sodium hypochlorite at high concentrations or for long periods. Levels vary seasonally with disinfectant use.

How can I reduce chlorate exposure?

Reverse osmosis is the most effective home treatment for chlorate, typically removing 80–95%. Anion exchange systems also work but require regeneration. Standard activated carbon filters provide only limited chlorate reduction. Boiling does NOT remove chlorate.

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