the problem with water in your iso is not so much a slower evap time (water evaps reasonably fast, especially when over 90% of it is alcohol), but rather the fact that water is more polar and MIGHT pull some impurities.
really it shouldn't matter all that much, tbh.
also filtering the iso definitely won't hurt, so if you want to, you most definitely can.
also also, make sure to evaporate in a very well ventilated space.
when its all evapped, i like to add a little bit (you don't need much) more water and re-evap to dissolve any leftover alcohol in the water, and evaporate it cleanly.