Xylenes

This is nasty stuff that comes from the gas refining process, paints that have been poured down drains, inks and detergents.

Xylene Related Health Problems include damage to the kidney, liver and nervous system.

The only way to tell the Xylene content of your water is to have it tested, but treatment generally involves water treatment with a quality activated carbon filter.

Most of the time sulfur contamination comes from decayed organic matter, but it can also be a result of septic contamination, chlorine, gasoline or hydrogen sulfide.

You'll know the water is contaminated with sulfur because the smell of rotten eggs is unmistakable. Treatment is as easy as using a good water filter, but if you have a persistent sulfur problem (like from well water) you should disinfect the well. Sometimes bacteria build-up in the well can smell like a sulfur issue.

Chlorine

Yes, of course you're going to have chlorine in your water if you live in the city. But with other contaminants being more concentrated as the drinkable water supply diminishes (during droughts, etc.) more and more chlorine is used to clean the water.

Chlorine can be detrimental to your health in many ways - some even say by causing cancer. You can taste the chlorine in your water, but you may have become so used to the taste you might not notice. Drink filtered water for a few weeks (not bottled because we care about the environment, right?) and then go back to your tap water. With a fresh palate you should be able to tell.

Removing chlorine is easy with either an activated carbon filter or reverse osmosis. For more info on R.O. check out Reverse Osmosis for Dummies: http://www.cleanwatercleanair.com/reverse-osmosis-for-dummies/.

Generally speaking, Iron isn't going to harm you. However, it is a heavy metal that can build up in your system if you take in too much of it. Iron comes from natural deposits and from rusting pipes and fixtures. You'll know it's an issue if your water is a rusty color or if you have reddish-orange stains in your sink.

There are many treatment options for iron contamination, including oxidizing filters, water softeners and carbon filtration.

Like iron, copper isn't going to kill you but it could give you some gastrointestinal problems. Copper contamination comes from industrial sources like wood preservatives, but also from natural sources and your plumbing.

You can taste copper, but not as easily as you taste some other contaminants. The only real way to know the level of copper contamination in your water is to have it tested. Treatment includes reverse osmosis, electrodialysis and the use of polyphosphate filters.

Other water contaminates include microorganisms (like Giardia), Bromate (causes cance), Total Trihalomethanes (Causes liver and kidney disease), Arsenic (used in rat poison), Barium (increases blood pressure), Cadmium (from corrosion of galvanized pipes) and many others, all of which can be found on the EPA's website: http://www.epa.gov/safewater/contaminants/index.html