Kidneys could have had a lot of calculi but if they were one solid mass in both you would have been in a pickle.
Viscous urine indicates a loss of electrolytes mainly potassium,but also sodium ,calcium ,magnesium,phosphate.Not just the calculi sediment.
Too long a fast will deplete be cautious.Kidney inflamation could cause you to feel you could not bend over but soft tissue won't harden.Unless you are Lot's wife.
Remember distiiled water is best also mix with veggie or fruit juices. Short fasts with emphasis on keeping lots of electrolytes in the body even during fasts.Also divide weight by 2 and drink that many oz/day.eg 200lbs/2=100 oz =12 (8oz glasses)over 256oz means you have to weigh over?Drinking 4 oz every half hour through out the day is better than large quanities.