in your case, i wouldn't even worry about it. your extract already had the mineral content needed when it was created. chlorine in water is feared more than it needs to be.
I brew with chloramine treated water...which doesn't evaporate at all...it has to be chemically bonded/removed. But I don't even bother, and so far no one has noticed any chlorine related off flavors in any of my extract, PM or AG brews.
If you' can't sleep at night though, go ahead and use spring water from the grocery store...NOT reverse osmosis or distilled water though...its too mineral deficient.
Primary: English Mild
On tap: Pale Ale, Lancelot's Wheat, English Brown Ale, Steam Beer, HoovNuts IPA
Bottled: MOAM, Braggot, Raspberry Melomel, Merlot, Apfelwein, Pyment, Sweet mead, Cabernet
Gal in 2009: 27, Gal in 2010: 34, Gal in 2011: 13, Gal in 2012: 10