We talk about this so often on this forum. A quick search about "using tap water" would bring up the threads.
We can't tell you what to use in your tap water because we don't know anything about the source for your area.
Are you on a private well? If so, do you use any filters, water softeners or other treatments on the water before it get to the tap? Do you have problems with hard water stains or calcium buildup? These won't really hurt your cham, just need more cleaning. If your well water is safe for human consumption your cham should be OK too.
Are you on municipal water? If so, you need to call your water utility and find out what they add...fluoride, chlorine or chloramines. Only then can you decide what if anything you need to add to the tap water before using for your cham.