Plastic may absorb the pop, but it doesn't sour. It will only make your water taste a little sweeter. Glass containers will break in some emergencies so carefully consider where to store it. Rotate your water storage at least once a year. Remember, when water is exposed to heat or light for long periods of time, algae and bacteria can grow in it.
Tap water is generally okay to store, but there is no guarantee that it is bacteria free.
You cannot, however, use water from swimming pools or hot tubs. Different sources recommend different amounts of water per day. I've heard as little as 1 gallon per person per day, or as much as 7 gallons per person per day. Just remember, the more you have, the more comfortable your situation will be. Consider your own family's special needs such as if you have babies, nursing mothers, ill persons, or little children who may need more water.