I’ll drink straight from snowmelt and springs or seeps. But we boil most other sources. Some of the silty streams in canyon country will plug any filter almost immediately. The issue there is boiling might not be enough because of Cyanobacteria. The toxins are not removed by boiling and might be increased by rupturing the Cyanobacteria. So along our routes we look for springs and seeps and tend to carry more water than most folks do.