Application.
What are your total applications.
Self defense.
Hunting?
Get home.
The 9mm is a common round so availability is good.
Most likely you will have 1-3 mags fully loaded.
If you have a bulky get home bag it most likely will not be with you when you need it, plus a long gun and...
Lots of good information here:
https://www.cdc.gov/healthywater/emergency/making-water-safe.html
Read carefully about Cryptosporidium & Giardia.
I actually have experience in this field and my advice is filter and disinfect.
Filtering will help remove some total organic carbons, dirt &...
Sawyer and if I have time iodine or bleach treatment.
Filtering and boiling are best, I have extra coffee filters for this at home.
.1 micron filtration will get most stuff out but viruses need a .02 micron filter and it will be super slow.
So that is why I say 2 step system if you have time...