Just stumbling across older posts - late to the party as always.
Something you may not have considered about UV treatment - it does not kill the bugs in your water. UV light alters DNA so bugs can't reproduce. You'll find UV treatment descriptions like this: "UV light is normally effective against all viruses, bacteria and protozoa..." But, they are still alive when you swallow them. Yuck right. Other considerations are that cloudy water interferes with the UV light, so filtration is needed anyways. And "microorganisms such as Cryptosporidium and Giardia have protective or thick cell walls that some low power UV light systems are not able to penetrate."
The things I consider when filling up my container are: what's floating in it, what's swimming in it, are their chemicals in it?
->For floating things like dirt, plants and otherwise harmless media, I filter it.
->For swimming things like viruses, bacteria and protozoa, and microorganisms like as Cryptosporidium and Giardia, I boil it then filter it, OR use chemical treatments like chlorine or iodine, then filter it. (Boiling and chemical treatment work, but I don't like washing back dead bugs so I filter it afterwards.) I rarely use chemical treatments.
->For chemicals in your water like pesticides or other water treatment chemicals that have an unpleasant taste, I use an activated carbon filter in tandem with a water filter.
*For Chemical treatments like Chlorine and Iodine, it's important to note that other chemicals present in the water can react with your water treatment chemical and take it out of action (reduce its effectiveness). Also, chemical treatment requires specific treatment times for a given volumes of water, and is even effected by the water's temperature; the colder the water, the slower the reaction.
*Filtering your water is probably all you need to do, in North America as they say. But, strain it first. Don't clog your filter with puddle water, pre-filter it to an acceptable clarity. use a bandana, your shirt, get creative.
*Lastly: Seek good water sources. Don't filter puddle water.
There's so much to cover, this is just a small sample of what's out there. Know your area.
Sources:
Wilderness First Aid student handbook 2010
https://www.portablewaterfilters.org/water-filter-guide/particle-contaminant-size-chart-microns/https://ww2.health.wa.gov.au/Articles/U_Z/Ultraviolet-disinfection-of-drinking-water#:~:text=Yes.,are%20not%20able%20to%20penetrate.
