Tap water is already treated and is good for storing. If the container you put it in is clean then it should be good for at least 6 months kept in a cool dark place. If the container is new then add a gallon of tap water and some bleach. Swish it around and leave to cap loose so you get the threads as well. Best containers are those made specifically for this purpose. If you have to economise then use food grade plastic containers. 2 liter pop bottles well rinsed with a bleach solution are a viable alternative. IF you are concerned about quality when you go to use it then treat it with bleach and or filter it through one of the many good systems available. As in all thngs rotate your water supply. Use the discard for garden, laundry etc. Hope that helped.
Municipal tap water is actually safer than bottled water. It is highly regulated, more in fact than bottled water manufacturers. However bottled water often tastes better than tap water because tap water has a lot of chlorine in it.

