I have spent much time in remote areas in various parts of the world, and I have seen large areas with no clean water at all. I have seen "pristine" looking water in high mountains give serious gastrointestinal problems, resulting in very severe dehydration. Every tool you can obtain is an advance in the right direction.

Settling, or decanting as you call it, straining, filtering, chemical purification and boiling are all useful, and better in combination, if you have the time and resources.

I have also spent much time in deep jungle where I strained the water through a t-shirt and used iodine tablets, and had nothing wrong with me.