In general, symptoms may include headaches, dizziness, stomach and intestinal upset, numbness of extremities, spasms, convulsions, and heart attacks.  Some pesticides are suspected of being endocrine disruptors and causes for developing cancer, which would be long-term effects.  Some symptoms are acute (immediate) and usually appear after exposure to a large dose (like spilling it on yourself, accidentally sprinkling it on your food, etc.), more than you could get from groundwater contamination under most circumstances.  Other symptoms are chronic, which means they occur in the long term.  Each pesticide has a different set of possible health effects--to learn more, visit www.epa.gov/safewater/mcl.html#organic.

Also, the effects of mixing pesticides (consuming more than one pesticide at a time in the water) are virtually unknown.

Groundwater quality responds more slowly to changes in chemical use or land management practices than surface water.  Changes can lag from many years to decades.  So when groundwater becomes contaminated with pesticides, it may take many years to recover, even after the pesticide use is discontinued.