I only carry tabs or chemicals anymore but used to use a first need filter ( still have it stored in a sealed plastic bag if I feel I need it).
Utah--downstream from rotting cow carcass---used First Need---no problems
Gila--gray water from silt from burn runoff upstream. Settled, decanted 2-3 times, Aqua Mira for drinking, boiling for use with rehydrated meal---no problems
Utah--water in the Swell, will give you the trots no matter how you treat it. Lots of heavy metals, Minimal consumption and or mix with water you've packed in.
Ca--water with lots of squigglies in it, decant, use bandana, treat with chemicals and drink it. Look at it as some protein---no problems.
Utah--couple of springs sources no treatment, pay attention to how is acquired---no problems.
Wyoming--- used chemicals but took some water from glacial melt and did not treat---no problems.
Gila--water from spring with animal poop in it---chemical treatment and no problems.
I mainly pay close attention to hand hygiene and how I treat the water and it seems to work for me. I carry some instant lemonade mix to offset taste.