Drinking water is the definition of chronic exposure, it is generally consumed within a small physical boundary (home, city, metro), and makes up 65-90% of the human body depending on age/fitness/sex. Humans consume more water than any other substance by weight, it is our primary ingredient for life. Even those that shy away from a water bottle to a coke are made primarily of water, it permeates every cell in our beings.
So there is no getting around it, even if the water around you isn't the best, you're still consuming it, because if you don't you will die. Of course you can get better water easily via treatment or transportation.
There have been countless books written on the subject of contaminated drinking water and health, the topic is well researched. I will link resources here over time, but the core of my research has been on how to remove the widest spectrum of harmful contaminates. The largest challenge in modern synthetic contaminates removal is the extremely low levels at which they are harmful.
The Dose Does Not Make the Poison
Unlike traditional contaminates like lead or mercury, modern contaminates don't poison the body directly, they act on the endocrine system, mimicking hormones and disrupting the messages they are meant to pass around the body.
This means that minuscule amounts of EDCs can harm humans, working similar to radiation - where a single exposure can have lifelong consequences. Hormones either oversupplied or under-supplied during gestation can cause birth defects on their own, and other chemicals can epigentically alter DNA, causing cross-germ line changes and downstream effects in offspring.
Cumulative Effects
Many of the chemicals in the modern contaminate class do not leave the body via normal toxin excretion routes, they tend to build up in the body and only increase in concentration over time until exposure is controlled. Given that human drinking water use is extreme in volume, chronic and localized, exposure from dirty drinking water is a huge concern.
Diagnosis
The effects of the aliments caused by exposure to modern contaminates can take a long time to manifest, meaning that there will be a very slow build up of a given contaminant in the body for years prior to an symptoms presenting themselves. Once these effects have set in, they are extremely hard to reverse given how the body does not process and eliminate them.
In short the effects from contaminated drinking water consumption are not light, and there is no known treatment. Sadly this is a vitamin vs painkiller issue, with only knowledge and preparation being effective in mitigation.