Herbicides

What is Herbicides?

Herbicides are the weed-killing chemicals used on farms, lawns and roadsides — atrazine, glyphosate, 2,4-D and metolachlor are among the most common in U.S. water. They reach drinking water sources through rain runoff and groundwater seepage, so levels are highest in agricultural regions and spike in spring after application. Most public systems test for the regulated ones; private wells are on their own.

The health picture varies by compound. Atrazine is an endocrine disruptor that persists in groundwater and is banned in the EU but still widely used in the U.S., with an EPA drinking-water limit of 3 µg/L. Glyphosate is far less toxic per dose and has a much higher limit (700 µg/L), though the WHO's cancer agency classified it as a probable carcinogen in 2015 and the evidence remains contested. Long-term exposure to mixtures at low levels is the least understood part.

On a water filter, "herbicides" means the filter has been tested to reduce a representative set of these chemicals — usually under NSF/ANSI 53 for specific compounds such as atrazine. Activated carbon adsorbs most herbicides well; reverse osmosis removes them along with nearly everything else.

Commonly found in: Municipal tap water, Well water, Water filter claims, Lab-tested products

Sources: National Primary Drinking Water Regulations · Atrazine · Glyphosate