Consensus is that the must is homogenizing with the added water, so just wait for the SG to stabilize then use that as the baseline for ABV and pitch the yeast.
I've been making wines for about nine years, mostly kit wines but also country wines from Palisade peaches as well as mead. A couple of years ago, I bought a hydrometer that reports the specific gravity electronically, and noticed a strange (to me) phenomenon. After pitching the yeast, the SG...