Hundreds of thousands of snakes all across the country get water straight out of the tap from all different municipalities. If the standard chlorine included in clean drinking water were dangerous to snakes, they would be dying off in droves. Basically, if it's safe for you to drink, it's perfectly safe for your snake. No additives needed.
Edit for one more thought: And if one is still paranoid about chlorine in drinking water, you still don't need additives to remove it. Just fill a pitcher or bucket with water and let it sit out for a day. The chlorine evaporates out of the water.