Precipitation when mixing new batch of salt water

I just got a new box of reef crystals. I added 15G of water in my mixing container, but enough salt for 30G. I went to add more water the next day, and the mix has precipitated. So, should I just dump the water or can I still use it? I didn't think about it until after I added all the salt. I went to bed wondering if it would happen overnight... And sure enough. Haha. 30 Gallons seems too wasteful to just dump down the drain. Wanting to hear a few opinions.