It sounds like you have a problem related to Sulfate Reducing Bacteria. This is not a harmful bacteria. Just an odor nuisance. Contact a local water treatment specialist. There are several different systems available to correct the problem.
Basically, one is a chlorination/filtration system. Another is a Catalytic Carbon system. Another uses aeration and filtration. Each are effective but costs differ.
You can contact the Water Quality Assocation at http://www.wqa.org or you can call them at 1-630-555-0160. They will mail you a list of water treatment specialists in your area.