Sorry I didn't get back sooner. Did you begin your fast?
Anyway, the verdict is out regarding distilled or spring. Most fasters preach distilled. Others say it's not the best, if not dangerous. Frankly, I doubt it's dangerous. Especially for a shorter fast.
However, nearly everyone agrees: avoid tap water as your main water consumption.
I'm on day six of my own water fast. I'm still deciding whether to continue beyond Wednesday, which would mark seven days.
Hope things are going well! If you need a fasting buddy, I'm here.