Is your well water getting saltier?

Road salt seeps into the wells Massachusetts towns drink from. We read 33 years of state lab results to show which ones are rising, town by town.

Try , or

5,672 wells tracked

856 rising

49/160 crossings caught early

1995

The average town had 26% of its wells over 20 mg/L.

0%100%

Share of each town's wells over 20 mg/L, by each well's latest test in the ten years before. Hover a town for its numbers.

Sodium and chloride from treated roads soak into aquifers and stay. Each winter stacks on the last.

MassDEP publishes every well test as raw lab rows. Nobody had turned them into a trend per well.

It is the MassDEP sodium guideline for people on sodium-restricted diets.

One well, 33 winters.

The North Plymouth GP well went from 7.7 mg/L of sodium in 1993 to 127.0 mg/L in 2026.

Plymouth Water Department. Over 20 mg/L matters for people on low-sodium diets.

1

Pull

Every sodium and chloride result from the MassDEP Data Lake API.
2

Clean

Match each result to a well and a town. Drop look-alike chemicals and non-numeric rows.
3

Trend

Theil-Sen slope per well. Rising only when the Kendall test gives p < 0.05.
4

Warn

Flag wells under 20 mg/L that the trend carries past 20 within five years.

We hid every result after 2015, ran the warning, then compared it with what wells actually did from 2020 on.

111 missed, of 160 wells that crossed 20 mg/L 49 caught