Pesticides in well water: atrazine, 2,4-D and limits
Pesticides can soak into groundwater, especially in shallow wells near fields, orchards and lawns. Atrazine is the most commonly found. Above the limit, use another source for drinking and ask about a certified filter.
- US (EPA), µg/L
- Atrazine 3, simazine 4, alachlor 2, 2,4-D 70, glyphosate 700. Metolachlor has no EPA limit.
- Ontario, µg/L
- Atrazine (with breakdown products) 5, simazine 10, alachlor 5, metolachlor 50, 2,4-D 100, glyphosate 280.
What it is
Weed and insect killers used on crops, orchards, golf courses and lawns can move down into groundwater, especially through sandy soil and into shallow or older wells. Spills while mixing or rinsing sprayers near the wellhead are a common cause of high levels. Labs report pesticides in µg/L, the same as parts per billion.
What your number means
- Not detectedBelow the reporting limit
The result you want.
- Worth a lookDetected, below the limit
Retest, and keep pesticide mixing and storage well away from the wellhead.
- Above limitAbove the limit
Use another source for drinking and cooking, contact your health department, and ask about treatment.
What to do
- Above a limit, use bottled water for drinking, cooking and infant formula.
- Tell your health department, and check whether pesticides are mixed, stored or rinsed near the well.
- Ask about activated carbon or reverse osmosis certified for the specific pesticide.
- Check the well cap and seal, since shallow or damaged wells let surface water in.
How often to test
Once, and every few years if you live near farm fields, orchards or golf courses. Retest after any spill near the well.
Common questions
Which pesticide is most common in wells?
Atrazine, a weed killer used on corn, is the pesticide most often found in groundwater in farming areas.
Does boiling remove pesticides?
No. Use a filter certified for the pesticide you have, or another water source.
Sources: EPA drinking water regulations; Ontario Drinking Water Quality Standards (O. Reg. 169/03). Limits checked November 2026. We review these standards every month.