Step 1: Research

The first task is to identify the common contaminants found in municipal water. A quick google search provided the following resources:

EPA's list of regulated contaminants (this is pretty large...) or the Printable version 

US Geological Survey - Contaminants in Ground Water

Neilson Research Corporation - Common Drinking Water Contaminants

CDC's Top 10 Water-related Diseases and Contaminants in Public Water Systems

The following link was the top hit on Google, and also provides an abbreviated list, but I would rate the information in the "trust but verify" category.

Environmental Illness Resource - Common Chemical Contaminants of Municipal Water

This is a nice link; it allows you to search for your water system and you can find out what violations have been logged. This may help you make a decision to add some targeted filtration. My system had multiple violations of fecal coliform (last violation was 9 years ago) which may explain why we seem to have very high chlorine levels. I need to pay more attention to filtering chlorine.

EPA's SDWIS Federal Reports Search

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Step 2: Identification

What do we do with the plethora of information? There is obviously way too much to digest without being an expert, and the purpose of this is to get a simpler view of what exists in my water that needs attention. Another approach is to look at what people are verifying using available tests. The only way you will know if you need to filter something is to identify that substance in your water, both before and after filtration. 

The following list comes from a search for "water quality test" on amazon. These are the available tests that can be done with test strips:

• Free Chlorine
• Total Chlorine
• pH
• Nitrites
• Nitrates
• Bromine
• Bacteria
• Pesticide
• Total Alkalinity
• Total Hardness
• Total Dissolved Solids (TDS)
• Iron
• Iron Bacteria
• Copper
• Lead
• Cyanuric Acid
• Hydrogen Sulfide

Step 3: Breakdown

So now that we have list of what we can test for, we can "not worry" about the other stuff. Most of the stuff we can't test for is filtered to some level with whatever filtration we choose. Now we need to put the previous list into some kind of priority order. I'm going to do this for myself, but I'll list with each item why I chose it in that position. 

1. Free Chlorine
   
   1. This is probably the most concerning "contaminant". I say that because this is actually added in order to control biological contamination. This is the actual chlorine that is available to treat the water. This differs from total chlorine, which is the quantity of free chlorine along with the chlorine that has already bonded with stuff and is less able to treat other contaminants. 
   2. Chlorine is probably the number one item listed by health nuts to filter from your water, both for taste and for health reasons. It is easily absorbed through the skin as well as internally. There is quite a bit of anecdotal evidence (maybe some scientific, but I haven't actively researched yet) that various health conditions stem from absorption of chlorine. 
   3. This is also something you want to filter at the point of use, because taking the chlorine out of your water before it sits in your hot water heater you risk growing bad biological stuff in your water heater.
2. To be continued later (maybe years later... that's kind of how these things go for me...)