Since it's so dead and we need some fresh material, there's this, which might also come in really handy for some people planning trips during Sept (shoulder season is a nice time to go):
https://www.nps.gov/yose/planyourvisit/wildcond.htm
When you get right down to it, the water availability isn't really much different than any other year. Flows are most definitely lower (different for sure...YMMV) and you might have to work a little harder to get it, but roughly currently reported sources are generally the same as they always are this time of year. All things considered, I would still and always do tend toward strategically located lakes/rivers/major creeks as way points or destinations, but there aren't a whole lot of big, heavy, water lugging areas/stretches within the report that aren't entirely surmountable with a little proper planning and maybe an extra water bottle or two...and maybe the ability to use your pump well. For how detrimental and annoying this drought is, surprisingly not too bad within the scope of YNP's trail systems and the typical reports for early Sept.