Hydration is one of the most important considerations in the wilderness. Water is also one of the heaviest items to carry. One pint is one pound. In the most extreme cases one must carry all of the water needed for the course of the trip. Dehydration should be avoided at all costs and along with hypothermia or altitude sickness can be life threatening in the wilderness. In the dry and warm mountain air, combined with the effort required by backpacking, it is possible to lose water without even being aware of it. If you are thirsty, drink water. Have it in a convenient location to encourage drinking. I have helped search for older folks who perished after wandering off trail. Some have attributed it to high altitude dementia but I believe dehydration played a role.
When I consider a backpacking trip or even a day hike, I look at a topographical map to see if there are water sources along the way for resupply. Know where there is water along the way! Often a hike is to a lake where resupply is guaranteed. What I don’t want is to carry more water than I need or to run out of water too soon. Additionally because a creek is indicated on a map does not mean that it will be there in late summer. Some creeks are year round even in dry years however.
There are two main considerations for me. The first is what containers I will use and the second is what filtration I will need. Let me begin with containers. For years as a trail runner, I went with plastic bottles with pop tops on top of screw on lids. I used a double bottle fanny pack. When I ski the back-country I still stay with this combination. One thing that can happen in cold weather is the pop tops freeze. You can bang the bottle against a tree and unscrew the lid to drink. Even insulated hoses on bladders can freeze up.
I am still partial to bottles. Nalgene bottles seal well and are almost leak and bullet proof. I always carry two brightly colored bottles on backpacking trips. If one winds up getting lost, left behind or rolls down a cliff, you will always have a backup bottle. When there is easy access to water (trails that follow creeks), I only fill one bottle to save on weight. I use one bottle with a filter in the cap. This allows me to quickly resupply and move on with potable water immediately. I also carry chlorine tablets for the other bottle. Having two bottles also allows for a chlorine pill to do its work in a fresh resupply bottle while you drink out of the other bottle if you don’t have a filter bottle.
There are other means to carry water and perhaps bladders are one of the most popular. Most packs today are designed for bladders with a separate pocket inside the pack. I have backpacked with a few folks who swore by bladders. IF the bladder develops a leak or is improperly sealed, guess how long it will take to notice? Your gear may be wet by the time you feel the water dripping down your backside. Also, one is usually committed to filling the bladder once your pack is off your back. This may mean two plus liters of water added just before a big climb at altitude.
There are additional means for water purification like a pump with a filter, ultraviolet pen, and iodine pills. I have used these methods and each works better than boiling. What I do recommend is filtering or purifying your resupply water. There are bacteria and viruses even in a fast flowing mountain stream.