WHAT'S IN A GLASS OF WATER
Insecticides and herbicides can wash into rivers and lakes and seep into groundwater. The pesticide atrazine has been linked to hormonal imbalances in lab animals but probably isn't carcinogenic.
As rock erode, they naturally release fluoride into soil, air, and most water sources. Because it can prevent tooth decay by rebuilding enamel, many communities add extra to the drinking supply.
Water-treatment facilities add chlorine as a disinfectant, and it's safe at low levels. But some disinfectant produce byproducts that have been linked to miscarriage.
Arsenic occurs naturally in rocks and soil, and it's linked to increased risk of cancer. A water treatment plant should remove the poison, but private well owners must periodically test for it.
Naturally occurring and harmless, this chemical is still a pain the butt. It smells like rotten eggs, stains clothes, and corrodes pipes.
Old, corroded metal pipelines can deposit this patent neurotoxin into drinking water, as they did in Flint, Michigan. Children who ingest lead can develop permanent learning disabilities.
Agricultural runoff or warm water can stimulate fish-killing "algal blooms." But for us, algae in drinking water is just a nuisance, a musty, fishy taste that persists even after the treatment plant.
Everything from amoxicillin to Zyrtec makes its way, via your pee, into the rivers and lakes that supply our water. However, pharmaceuticals only contaminate surface water at extremely low levels.
You'll notice a medicinal taste or even greenish hair with just 1.3 milligrams of copper per liter of water. But the metal, which leaches from old pipes, is safer for humans at those levels. Just don't put it in your fish's tank.
Salts are a normal part of water, though a strong salty flavor can indicate a waste-water leak. And a high concentration of sodium or magnesium-sulfate salts might have a laxative effect.