There can be all sorts of nasties in tap water. Distilled is cheap, at least here. Less than a dollar a gallon. It's worth the expense, in my opinion.
As for keeping the water's pH up... It's probably best to use those calcium based sands and decorations, like aragonite/coral sand and/or coral decorations, fully cured, of course. Only those items will help keep the pH at the desired level. Anything else is temporary fix, at most, and are likely to cause problems in the long run.
Perhaps you can top off the sand in your container with some of those sands I just mentioned.