Chlorate Contamination

Chlorate in Pennsylvania Drinking Water

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

100

Cities Tested

Over HA

50%

% Over HA

299.3 µg/L

State Avg

▼ 9% vs national

vs National

487

Health Violations

Analysis

Chlorate in Pennsylvania: what the data shows

Pennsylvania has 100 cities with chlorate data from the EPA's UCMR 3 program (2013–2015). Chlorate exceeded the 210 µg/L EPA lifetime health advisory in 50 of those cities. The state average max detected level is 299.3 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)

Pennsylvania

50%

50 of 100 cities

← ▼ 9% below national rate (better)

National avg

59%

1866 of 3166 cities

City Map

Chlorate data across Pennsylvania

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 Pennsylvania

Highest Chlorate levels (µg/L)

All Cities

All Pennsylvania cities ranked by chlorate level

#	City	Level	Over HA?	Violations	Grade
1	Gettysburg	3730.0 µg/L	Over HA	37	F
2	Quakertown	1330.0 µg/L	Over HA	12	F
3	Tobyhanna	1030.0 µg/L	Over HA	10	F
4	Dallastown	970.0 µg/L	Over HA	3	B+
5	Bryn Mawr	838.0 µg/L	Over HA	36	F
6	Bloomsburg	833.8 µg/L	Over HA	6	F
7	Portland	690.0 µg/L	Over HA	5	B
8	Columbia	629.0 µg/L	Over HA	46	F
9	Mechanicsburg	610.0 µg/L	Over HA	13	F
10	Allentown	604.0 µg/L	Over HA	66	F
11	Wilkes Barre	570.0 µg/L	Over HA	2	B+
12	Southampton	525.4 µg/L	Over HA	9	D
13	Birdsboro	520.0 µg/L	Over HA	15	C
14	Philadelphia	503.0 µg/L	Over HA	14	B
15	North Wales	496.0 µg/L	Over HA	22	F
16	Newtown	488.2 µg/L	Over HA	25	F
17	Dover	432.0 µg/L	Over HA	16	F
18	Clearfield	411.0 µg/L	Over HA	3	A-
19	Oakdale	410.0 µg/L	Over HA	12	C-
20	Northampton	406.0 µg/L	Over HA	45	F
21	Jamison	390.0 µg/L	Over HA	1	B+
22	Tunkhannock	381.0 µg/L	Over HA	21	F
23	York	380.0 µg/L	Over HA	34	F
24	Yardley	380.0 µg/L	Over HA	1	B+
25	Lancaster	376.0 µg/L	Over HA	68	F
26	Easton	375.0 µg/L	Over HA	37	F
27	Pittsburgh	370.0 µg/L	Over HA	44	F
28	Mcmurray	370.0 µg/L	Over HA	2	A-
29	Cranberry Twp	360.0 µg/L	Over HA	2	B+
30	Warrington	359.0 µg/L	Over HA	34	F
31	Mc Connellstown	357.0 µg/L	Over HA	0	B
32	Reading	353.0 µg/L	Over HA	91	F
33	Harrisburg	327.0 µg/L	Over HA	26	F
34	East Stroudsburg	320.0 µg/L	Over HA	74	F
35	Coatesville	310.0 µg/L	Over HA	61	F
36	St Thomas	310.0 µg/L	Over HA	6	B
37	Norristown	300.0 µg/L	Over HA	23	F
38	Latrobe	291.0 µg/L	Over HA	4	B-
39	Moon Township	290.0 µg/L	Over HA	1	B
40	Sarver	290.0 µg/L	Over HA	9	C+
41	Lansdale	280.0 µg/L	Over HA	22	F
42	Whitehall	279.0 µg/L	Over HA	32	B+
43	Phoenixville	265.0 µg/L	Over HA	13	C
44	Kutztown	250.0 µg/L	Over HA	21	F
45	South Heights	245.0 µg/L	Over HA	1	A-
46	Elizabethtown	242.0 µg/L	Over HA	87	F
47	Clarks Summit	240.0 µg/L	Over HA	6	C-
48	Erie	230.0 µg/L	Over HA	35	D
49	Doylestown	230.0 µg/L	Over HA	4	D
50	Warminster	215.0 µg/L	Over HA	1	D
51	Spring City	200.0 µg/L	No	2	B+
52	Richboro	200.0 µg/L	No	2	F
53	Philipsburg	200.0 µg/L	No	1	C
54	Hummelstown	190.0 µg/L	No	35	C+
55	Waynesboro	190.0 µg/L	No	7	D
56	Grove City	170.0 µg/L	No	4	C+
57	Shippensburg	160.0 µg/L	No	11	D
58	Rockwood	160.0 µg/L	No	0	C
59	Pottsville	152.0 µg/L	No	13	C-
60	Charleroi	152.0 µg/L	No	25	C-
61	New Castle	150.0 µg/L	No	12	F
62	Fairless Hills	150.0 µg/L	No	15	D+
63	Sayre	150.0 µg/L	No	6	C-
64	Allison Park	141.0 µg/L	No	0	A
65	Sellersville	140.0 µg/L	No	9	F
66	Horsham	138.0 µg/L	No	1	F
67	Shamokin	110.0 µg/L	No	18	F
68	Jefferson	110.0 µg/L	No	2	A-
69	Milroy	101.0 µg/L	No	2	B
70	Johnstown	98.0 µg/L	No	55	D
71	Mount Joy	90.8 µg/L	No	8	B+
72	Emmaus	78.0 µg/L	No	16	C+
73	White Haven	75.7 µg/L	No	44	F
74	Chambersburg	71.9 µg/L	No	49	F
75	Fredericktown	70.1 µg/L	No	85	F
76	Blairsville	68.0 µg/L	No	22	F
77	Landisville	65.7 µg/L	No	2	B-
78	Matamoras	65.4 µg/L	No	1	D
79	Saint Marys	65.2 µg/L	No	10	B-
80	Williamsport	62.9 µg/L	No	19	F
81	Meadville	62.0 µg/L	No	21	F
82	Lititz	50.6 µg/L	No	73	F
83	Natrona Heights	49.5 µg/L	No	12	B-
84	Altoona	49.0 µg/L	No	64	F
85	Mcmurry	48.0 µg/L	No	3	A
86	Ambler	47.7 µg/L	No	4	F
87	Huntingdon	40.7 µg/L	No	14	B-
88	Levittown	39.6 µg/L	No	4	B
89	Greensburg	39.0 µg/L	No	19	D
90	Uniontown	38.0 µg/L	No	0	A-
91	East Greenville	37.9 µg/L	No	9	F
92	Pottstown	36.9 µg/L	No	29	F
93	Milton	35.0 µg/L	No	15	F
94	Windber	35.0 µg/L	No	0	B-
95	Ambridge	31.0 µg/L	No	19	F
96	Franklin	29.5 µg/L	No	12	F
97	Hazleton	25.2 µg/L	No	6	D+
98	Aliquippa	24.0 µg/L	No	9	F
99	Dunbar	23.0 µg/L	No	12	B+
100	Danville	20.5 µg/L	No	3	D

FAQ

Frequently asked questions about chlorate in Pennsylvania

Is chlorate in Pennsylvania tap water dangerous?

Chlorate has no federal MCL. The EPA lifetime health advisory is 210 µg/L. 50 cities in Pennsylvania 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 Pennsylvania 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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