Answer:
William's father meant that the hatred, segregation and prejudice they experienced in the hands of the white people will not continue forever but there will be a day when they will not experience it again; it will be a time when the white people will no longer segregate.
Step-by-step explanation:
From A Tale Of Segregation, William Minner remembered how his dad was humiliated and treated when they wanted to get water. The white people prevented his father from fetching water. They decided that William's father must wait until all the white people have taken theirs. William's father had to wait until the white people fetched their water. Then he said to his son, "But this is not going to be forever . . . There's gonna come a day when this won't be anymore."