Here's a common scenario: farmers need to get rid of slurry, so they spread it on the fields (behind the house).When it rains the slurry seeps into the aquifier and bingo, water source becomes contaminated!
Worse is:
https://www.scientificamerican.com/article/drugs-chemicals-seep-deep-into-soil-from-sewage-sludge/
farmers are paid to take this waste, or they are tricked into thinking it is environmental friendly and even pay for this. It is full of poisons (lots of research to back it)! and it indeed pollute ground water and soil (and likely also crops)
"a variety of chemicals, including anti-depressants such as Prozac and hormone-disrupting compounds in antibacterial soaps"
"Triclosan was found at the highest concentrations in the deep soil"
"Triclosan also has been linked to altered thyroid hormones and estrogen-related reproductive effects in animal studies. "
organic from farm animals are "fine". just buy filter for viruses, bacterias and parasites... all the chemicals in sludge hard to prevent if dumped on fields, the numbers of different chemicals there are many.
The water quality in many places in so called advanced western civilizations are horrible... asbestos (from pipes), prozac, hormon disturbing ingredients...common many places. bottled water not necessarily better.