Thanks for the advice re: using ice. The odd thing is that Midwest actually suggests it as a possibility in their kit recipes. And nowhere do they even mention using either filtered or boiled water for the top up, though it makes complete sense (which is why I asked). Most everything I've made has been darker beers, with the exception of a honey ale. All brewed with tap water and mostly using ice. There's an old brewery in St. Paul (the old Schmidt/Landmark) brewery and I think even though it closed, you can still get water there. I'm considering going over there with some jugs and attempting a brew using that water.