A very strong sulphur odor comes from our basement ,when ever it rains and when we do laundry, our Home is only three years old ,the land around us is mostly clay bed, we have a well, but we invested $7.000.00 into a water purification system so we are able to drink our water ,We have a septic bed as well.We have closed in the sump pump room, and installed an exhaust fan.But we still get a bad sulphur odor.I am getting sick of the smell. What more can we do to get rid of this odor?

Any possibility of Chinese Drywall?
http://www.chinesedrywall.com/

we invested $7.000.00 into a water purification system
Was the reason for this system a sulfur smell from your well water? If so the ground water that your sump pit collects may be the stinky culprit.
Consider enclosing the sump pit and see if that doesn't help. Good luck, Tom