It would be impossible to eliminate all chemicals and microbes from drinking water, right? Rather than elimination, the EPA often sets standards of "allowable" levels of chemicals and microbes in the water supply. For example, a chemical used to kill weeds, atrazine, has been considered safe when the yearly average does not exceed 3 parts per billion and the daily dose remains under 297 parts per billion.
New evidence suggests that atrazine may be particularly harmful for the babies' development. While still in the womb, dosages exceeding just 1 part per billion were associated with low birth weight and birth defects (if you find this article please pass it along!). In animal studies, atrazine exposure has been associated with development of cancer. Epidemiological studies suggest that there may be increased rates of some cancers, including prostrate cancer among people with close contact with atrazine, as well.
The most recent EPA document on the health concerns of atrazine (dated October 31, 2003) states that
"the Agency does not find any results among the available [epidemiological] studies that would lead us to conclude that a potential cancer risk is likely from exposure to atrazine."This statement is echoed in their July 2009 Status Update.
It seems like common sense to assume that any chemical that kills weeds would be safe to consume, and that the fetus of a pregnant woman may be particularly vulnerable to such exposures. To determine a cause-effect relationship here is extremely difficult, however. This is because the most convincing way to "determine" causality is to conduct a randomized-controlled trial, which would require subjecting some women (pregnant women?) to be randomly assigned to receive potentially dangerous dosages of atrazine.
The UK has banned atrazine because of how easily it contaminates groundwater. What is keeping the US from doing the same? Is there a safer alternative? Or has our dependence on industrialized farming found yet another cause for public health concern?