MC and over worked kidney

I was told by my naturopath physician that I have an overworked kidney and this worries me since the Master-Cleanse requires you drink so much water. He actually only wanted me to drink 2 cups of water, 2 cups miso soup and 2 cups herbal tea a day.

How do you think the Master-Cleanse works if you have an over worked kidney? I don't even really understand what it means to have an overworked kidney... Any thoughts are appreciated.