Our first goal is WATER STORAGE.
You should have chosen a type of container(s) for water storage as well as a location(s).
Begin collecting or purchasing those containers.
This might be a one time purchase or especially in the case of pop bottles, an ongoing endeavor. Containers should be food-grade and clean. You can store an assortment of container sizes and put them in many different places. In an emergency, having a variety might give you some flexibility as you use your water.
A siphon pump and wrench (to open the seals) may be helpful for use with the large barrels. These run from $5 to $10. They are not necessary, just helpful. It's not very convenient to tip these barrels just to extract a little water. The siphon pump allows you to leave the barrels upright and move the water into smaller containers. I didn't have a specialized wrench for a long time and would just use the side of my hammer to open the seals.
See previous posts on water for sanitizing methods. (http://iprepared.blogspot.com/search/label/Water).