There is a depressing shift toward hikers carrying disposable, single use, bottles of water. Single use water bottles are one of the biggest frauds visited upon the American public. Much of the time, the water is merely tap water, not spring water. If it is spring water, it has been shipped a long distance, adding to the carbon cost.
Most of the time, these bottles are not recycled, and more than two-thirds of these bottles end up as landfill. Those which are "recycled" are actually "down cycled" They cannot be turned into other bottles: they are fashioned into items such as picnic tables or fleece fabrics. The process uses some nasty chemicals as well.
The rationale seems to be that these bottles are light. True. However, they are disposable. One may purchase soft water bottles from such companies as Platypus and Nalgene which are just as light and have a lifetime guarantee. The environmental load of these bottles is outrageous, and backpackers should eschew them.
Water along the trail must needs be treated. Back in the day, one could drink water with some impunity. Now with masses of persons entering the backcountry, not so much. Also we now have giardia, which is spread by beavers, deer, and dogs.
One may purify water by boiling. Heating water to 180 degrees for one minute will kill the nasties. However this takes a lot of fuel and time and is impractical on the trail.
Chemicals include iodine and chlorine. Ordinary bleach works, but can take a lot of bleach if the water is cloudy. Clear water requires two drops of bleach per liter and a half hour wait. Chlorine will bind with organic material, so dirty water may not purify.
Iodine kills things rapidly, but many people do not care for the taste.
Adding vitamin C to water can absorb some of the chemical taste.
Filters force the water through a physical barrier and take out large baddies. This will not work for viruses. Filters are heavier than chemicals, but one can drink the water immediately. A filter of 0.4 microns is sufficient for hiking in North America. A micron is 1/1000 of a milimeter. Hiking in other countries, or if one wishes to rid the water of viruses, may require a commercial filter, like the Katadyn professional which has an extremely efficient filter, or use of a filter and iodine, or a filter impregnated with iodine.