Chloride in well water
The county where Chloride is found above the limit most often is Rockingham County, New Hampshire: 5% of 3,020 private wells tested, according to NH DHHS.
Chloride mainly comes from road salt and water softener discharge. Above 250 mg/L water tastes salty and corrodes plumbing. Rising chloride in a well usually means road salt is reaching the aquifer.
- Nuisance level
- 250 mg/L
- New Hampshire level
- 250 mg/L
- CAS number
- 16887-00-6
Where chloride is worst, by homeowner tests
Counties ranked by the share of private wells above the state guidance level in tests homeowners sent to the state lab. Shares combine town summaries, weighted by wells tested.
| County | Wells tested | Above state level | Highest | |
|---|---|---|---|---|
| Rockingham County, New Hampshire | 3,020 | 5% | 2,490 mg/L | |
| Belknap County, New Hampshire | 1,725 | 4% | 2,140 mg/L | |
| Strafford County, New Hampshire | 560 | 3% | 1,300 mg/L | |
| Hillsborough County, New Hampshire | 3,631 | 3% | 1,300 mg/L | |
| Cheshire County, New Hampshire | 639 | 3% | 660 mg/L | |
| Carroll County, New Hampshire | 1,832 | 3% | 1,300 mg/L | |
| Merrimack County, New Hampshire | 4,897 | 3% | 3,300 mg/L | |
| Grafton County, New Hampshire | 2,688 | 2% | 1,800 mg/L | |
| Coos County, New Hampshire | 623 | 1% | 670 mg/L | |
| Sullivan County, New Hampshire | 738 | 1% | 830 mg/L |
By individual samples
Counties with at least 30 individual samples in public monitoring data, against the EPA limit.
| County | Samples | Detected | Above EPA limit | Median |
|---|---|---|---|---|
| Franklin County, Maine | 30 | 100% | no limit | 1.91 mg/L |
| Cumberland County, Maine | 380 | 100% | no limit | 29.1 mg/L |
| Washington County, Maine | 79 | 100% | no limit | 3.8 mg/L |
| Somerset County, Maine | 57 | 100% | no limit | 4.21 mg/L |
| Penobscot County, Maine | 64 | 100% | no limit | 6.1 mg/L |
| Kennebec County, Maine | 44 | 100% | no limit | 15.1 mg/L |
| Hancock County, Maine | 41 | 100% | no limit | 4.43 mg/L |
| York County, Maine | 90 | 99% | no limit | 9.4 mg/L |
| Androscoggin County, Maine | 60 | 98% | no limit | 3.56 mg/L |
| Aroostook County, Maine | 88 | 97% | no limit | 9.25 mg/L |
| Oxford County, Maine | 206 | 96% | no limit | 6.9 mg/L |
| Rockingham County, New Hampshire | 356 | 95% | no limit | 26.7 mg/L |
| Cheshire County, New Hampshire | 101 | 92% | no limit | 10 mg/L |
| Strafford County, New Hampshire | 106 | 90% | no limit | 9.65 mg/L |
| Hillsborough County, New Hampshire | 229 | 85% | no limit | 11 mg/L |
How to test
Use a state-certified lab and a proper sampling bottle; hardware-store strips cannot measure chloride at the levels that matter. Collect from the kitchen tap before any treatment, and again after treatment if you install it.
How to treat
- Point-of-use reverse osmosis
- Distillation