Removing Dirty Water Stains from White Jeans

I don't have a solution, I think the reason the spots won't come completely out is because there is a possibility that there was automotive oil that had leaked out of cars, mixed in with the water. I used to have that problem too, whenever I wore any light colored pants to church and had to walk across the church parking lot, after it had rained just a little bit, it seemed like there was always just enough moisture on the concrete, that it splattered up on my pants, even though I was wearing high heels.