I assume you mean 500ml?
I never did quite get the hang of this new-fangled metric system!
I often used to suffer terrible cramp, particularly in the summer, if I walked all day long. I've always taken on plenty of fluids but it's adding electrolytes that has solved the cramp problem.
I wish they cured mine. I get it in the back of one thigh or the other, it starts about ten minutes after I've got in my sleeping bag, just as I am dropping off to sleep, and it leaves me thrashing about in agony till it's gone. It's a good job I camp solo because if anyone heard me in my tent they'd wonder what I was up to!