I hiked the PCT in 2006 which was a heavy snow year-----personally I used chemicals the entire way (Aqua Mira) when I felt that I needed to purify which was less often as the days went by---while there are bad sources of water in SOCAL this is overblown a bit---most of these cattle troughs people speak of are filled from a nice spring and you can usually get water from there---not always but in most cases. In the Sierras it makes no sense to boil or to melt snow---you will not be camping in the snow unless something goes haywire one day. Even in 2006 it was never necessary to camp in the snow---certtainly the passes we snow bound but the southern facing slopes were snow free below the passes. I also would say that many folks were very diligent (including me) about purifyi8ng water in the beginning and many were not so later on.