https://www.yahoo.com/news/us/articles/dozens-hikers-suddenly-fall-sick-211249845.html

> norovirus

Interesting. The most common water treatment method on the trail is a 0.1 micron Sawyer filter. That handles parasites like giardia, bacteria like salmonella and so forth, but of course does not handle viruses.

Some people use UV treatment, which kills everything, but doesn't filter out sediment and similar contaminants.

> drinking from sealed water bottles.

Which may be the most useless hygiene advice ever given to hikers. Let me just carry 5 gallons in sealed bottles for the next 100 miles of trail.

The military used to have water treatment (chemical) tabs for troops in the field, probably still do, but I don't know what bugs they kill.  Still better than nothing.

In an emergency, iodine, so many drops per gallon, will add some protection but I forget the ratio.