very time sensitive- boiling potatoes

Hi everyone!
I'm having a big luncheon in a few hours. One of the dishes is mashed potatoes. I asked a while ago if I could peel the potatoes the night before to save time today, and many people said yes, do that, and soak them in water.

Now my question is: Do I boil the potatoes in this water they have been soaking them in all night, or do I drain and cover with new water?