As Hikermor says, boiling is better, but it is difficult to fit a pot in your pocket. The advantage of this is the form factor, it has a pre-filter to get out the larger solids, and it has a sturdy pouch to carry the water, and it has grommets to tie cord to that helps you carry it, and also has a flat bottom to help it stand. It is not the best method for purifying, nor is the container the best thing out there. It is the best option I have found that fits in your pocket.

Regardless of what equipment you use, straining or filtering helps ensure cleaner water (certainly more palatable) and removes obstacles to the effectiveness to the chemical treatments.

Boiling always works, but requires a container to cook in and a fire or stove.

Chemical methods work but you need to filter and carry the water.

One thing that is lacking from most commercially available, pocket survival kits, is a water container. This is a good size one that folds up and fits in your pocket, and comes with a complete kit. The cost is not high. I will include this in pocket or backpack kits. The good equipment you have with you is better than the perfect stuff that you don't have with you.