I was on Monadnock and many of it's lesser traveled side paths Sunday and it was extremely dry but there was still at least a trickle in official brooks. I haven't done the MSG in it's entirety (I've done maybe 2/3 of it over the years) but I recall numerous sources that I'd expect will have water no matter what, i.e. ponds, swamps, significant streams, etc. So with the right water filtration set up I'd think you'll be fine.