Our fresh water tank doesn't drain completely, so there is always some water left over the winter. I have never noticed any indication of algae or bacteria growing in there when I sanitize the system in the Spring. I would think that it would be much more likely that bad stuff would grow if the RV was stored in a warm or hot climate for a long period of time.
Chlorine bleach decomposes over time, so it isn't going to last the Winter. The alcohol type RV antifreeze might provide longer term protection from bad stuff, but some folks are concerned with damage to seals with that antifreeze formula.
If you are really concerned, sanitizing the water system to kill off any bad stuff before you winterize should do the job, especially for your cold upstate New York location.
