You are hereAT
I will assume that you went to college and that you can conduct basic research.
Read what SECOR has to say (author of High Sierra). Read what the UCLA biologiical research has shown.
When people get sick it is a 99% chance that they poisoned themselves due to poor hygene. It is not the water. It is not the water. Really, it is NEVER the water.
The bigger question is why do humans continue to make serious and important group think mistakes?
1) Way Comfortable
2) Lots of compartments - organize gear = safer trip
3) Where Have I used mine - 1000 miles AT, 1000 miles PCT, GLacier NP, Whites, Gila. 20 years duration.