BlackOvis offers a variety of water filtration systems. The goal is to find the one that works the best for you. Water filtration pens, bottles, gravity bags, and pumps are a good option because there is a physical filter that removes material from the end consumed product. Some can even remove or reduce the number of chemicals in the water. However the filters on all of these have a limited lifespan and require cleaning and eventually replacement.
I first discovered gravity filtration bags while at the Mountain Warfare Training Center in Bridgeport California and have used them ever since. I like the ability to fill the bag, hang it and forget it, then return and have clean filtered water. I also prefer a hydration bladder to carrying a cup or bottle because you can carry more water and you're not occupying your hands and don't have something dangling off your belt. A hydration bag on your back also frees up your hands to use trekking poles while still giving you access to water as you move.
The only place where I have had issues with a filtration bag was on the southern part of the Green River here in Utah. The southern part of the Green was very low when my family and I went on a river trip last summer. The river was moving slow and we had to row the majority of the trip. The water was also the color and consistency of chocolate milk. As you can imagine this was not ideal for a bag. The bag would filter water but it did so slowly, and we had an alternative water sources, so I thought it better not to totally clog and ruin my filter. Other than this circumstance of extreme silty water I find gravity bags to be the most convenient method of water filtration for my purposes.
New UV pens are lightweight and can be used many times however they don't remove any physical material from the water you consume. While the water may be clean the taste and texture may not be the be the best, unless you have pretty clear water already.
While effective, by far the most unpleasant method of water purification is Chemical tablets and Iodine. They do nothing to filter the water and only act to make it safe but also unpleasantly drinkable. The benefit to chemicals and Iodine is that they are lightweight, compact, and effective. Chemicals and Iodine may not make the water taste great but they will make it drinkable which could save your life.
There are a variety of ways to filter water more naturally, these include boiling, distillation, or making of a natural filter. However these are all very time consuming, and do not always yield much water. Having the proper water filtration system that works for you will improve the quality of your outdoor experience and ensure your safety.