Can we rent part of park for nonprofit organization picnic? If yes can we grill and have drinking water availability their?

To the best of my knowledge you should be able to just go, I havent heard of anyone reserving anything there. As far as food, you can definitely bring food and drinks in, just be sure to take all trash out with you. I would call DCR regarding grilling there. They would be able to answer your questions better.

I'm fairly sure you don't have to rent it, you just need to reserve it.