Drugs can very difficult to remove, and water treatment facilities are only able to remove roughly half [https://www.scientificamerican.com/article/only-half-of-drug...].
In fact, one of the pills is made of urine: "The estrogen-replacement drug Premarin, prescribed to menopausal women, is made from horse urine; in fact, the drug's name is short for PREgnant MARes' urINe".
Since that the majority of female in the West are on birth control pills[1] that means that a lot of the urine in our water systems is in fact "pregnant urine".
1: "In the United States 98% of women have used birth control at some point in time and 62% of those of reproductive age are currently using birth control." - https://en.wikipedia.org/wiki/Prevalence_of_birth_control
About 16% of childbearing aged women in the US use the pill [1]. Even if you add all methods that can be hormonal (some IUDs are, not aren't), it's only 27.8%. Almost 40% of childbearing aged women in the US use no birth control at all.
For this discussion it doesn't matter that much. The quantities in the water supply that aren't being removed are a problem. In other contexts it might not be useful to think that nearly every woman who isn't a child or elderly is on the pill.
[1] https://www.guttmacher.org/fact-sheet/contraceptive-use-unit...