Researchers used to suggest that most of the synthetic hormones contained in oral contraceptive pills eventually found their way to public water supplies. While this may be technically true, recent research has shown that most of the estrogen found in public drinking water does not come from “the pill.”

A study published in the journal Environmental Science and Technology determined that ingested birth control hormones account for less than 1 percent of all the natural and synthetic estrogen found in public water.

Previously, figures were much higher. An article published in the magazine Herizons estimated that between 50 and 90 percent of all birth control hormones pass into public water. However, the article failed to account to the pill’s total contribution to water-borne hormones.

The new study’s authors clarified that water treatment plants eliminate nearly all of the main hormone, called 17 alpha-ethinylestradiol, that is found in oral contraceptives. They suggested that the estrogens found in water come from soy products, animal waste and human urine, which always contains some level of estrogen.

Excess hormones in water may lead to fertility problems, among other potential health issues.