Stored water needs to be changed every 6 months. Now is the time to do that, before it gets too cold and makes for a miserable job.
If you don’t have water stored for an emergency, NOW is a good time to start! You should have food, water and supplies to last at the VERY LEAST 3 days, but 7 days is more optimum and more if you can.
Water needed:
1 gallon/per person/per day
Keep stored water away from sunlight and don’t store in plastic milk containers. Plastic 2-liter soda bottles are ok to start with but can be cumbersome to store as well as replace. You don’t want to refill these as they are not made for indefinite use. You can buy small to large barrels for water storage.
I don’t know about refilling 2-liter bottles, especially with tap water. I’d invest in some already-purified gallon jugs. They’ll last much longer as long as you don’t break the seal.