To get rid of the sulfide smell, they either run it through a carbon treatment (the same as the water filter in a Britta) or aerate it...but that puts the smell in the air and people complain that it smells of rotten eggs. If your water smells funky, like rotten eggs or like chlorine, all you have to do is either 1) run it through your filter or 2) let it sit out for a while and the sulfer and chlorine will evaporate out of the water.
If you imagine all the pipes it takes to get tap water to your house and every other house and apartment where you live, that's a lot of pipes! And of course, they are all aging. That leaves a lot of possibility for e.coli (which I am assured is everywhere) and other water critters to get into the water, so that is why the chlorine is added, to kill it all.
A person with their own well water doesn't have water that goes through as many pipes, but they do not have a water treatment and monitoring system in place. I'm told they should have their water tested by the city/county (something), once a year. I think that's smart anyways. You don't know if your next door neighbors aging septic tank is leaking into the ground water you drink. Or your own septic tank for that matter! Or what if the farmer next door who sprays chemicals on all his fields, and those chemicals get swept into streams, lakes, and into the ground water. Or you live in the woods and you and your neighbors are red necks, or you are not, and you have a forgotten about diesel tank leaking diesel fuel everywhere. By testing your water, you will know what's in it. (duh.) In these situations I always think about Erin Brockovich. She's pretty great.
I'm thinking someday I may go into government utilities (electric, water, wastewater, etc) as a job. I think I would enjoy that. I would want to be in the public outreach department or in the lab doing the testing.
For the longest time I thought that a drinking water treatment plant got their water from the waste water treatment plant. That is not true, except in one town in Texas. I think Bear Grylls lives there.