High on any emergency evacuation bags' list of contents should be water. The challenge that arises is that water is heavy and takes up space. If you wind up on foot...there is a limit on the amount you can physically carry...or will want to risk carrying in your efforts to not become physically exhausted. Another thing to consider...is that once you have expended that water as you sit in a shelter...or consume it on your journey...you will need to look for water again.
When you find that water...it may be from a questionable source. Does it have fecal matter in it? Even if it does look clean...what bacteria or other spook may be in it?
A level of piece of mind can be attained by having a portable water filter of some sort in your pack. This is a big topic. I could get into boiling water. Iodide. Microns. The difference between purifiers and filters etc... You can learn some about that here.
I just wanted to point out something interesting to be found at church distribution. They now offer the Seychelle water filter bottle. This is interesting because...I don't recollect the church ever having any preparedness items for sale...other than food storage. This is not the cadillac of water filters...but it is a "good" filter. While it is currently sold out...it will be available for $16.50...with free shipping!!! The manufacturer is offering it for $29.99...plus you have to pay for shipping. Literally half the price if purchased from Church Distribution.
For that price...this would be a good one to have in a car emergency pack...a work emergency pack...or your regular home emergency evac bags. You could probably afford for everyone in your family to have their own!
If you have the money to purchase something that takes out more of the bad stuff...I'd recommend the first need.