What constipation? If you don't eat junk, just tabs you have no stool forming at all, and no constipation I agree, everything depends on the overall health of your digestive system. So, perhaps if in a doubt it would be better to discuss the Survival tabs use (or any other survival food as well) with your doctor first. Regarding the water intake, it's enough to follow the 30 minutes (or more) rule to avoid any trouble.