Pesticides can move into ground and surface water sources through different
means, depending on their chemical character. Soluble pesticides can percolate
through the soil and reach groundwater while volatile pesticides may move into
the air and be deposited in surface water. Some pesticides will remain strongly
bound onto soil particles and are therefore less likely to move into water
sources. Pesticides can also reach surface water sources directly through
spills or improper chemical spraying practices. Once in the aquatic
environment, pesticides can cause harm to aquatic invertebrates and other
species, and destroy aquatic plant-life.
According to the Canadian Water and Wastewater Association, pesticide contamination of drinking water is also a serious problem. At present technologies can lower pesticide concentrations in drinking water to acceptable levels, however the increased presence of contaminants could eventually require a change in water treatment processes, which would entail high costs and, according to the Association, would produce not particularly satisfactory results. For more information on this issue see Pesticides in the Aquatic Environment (Standing Committee on Environment and Sustainable Development).
Other websites with information on Pesticides and Water Quality:
Clean Water for Salmon Campaign (NCAP)