Hi, Thanks for writing in. An overactive bladder is usually due to the muscles at the bladder mouth, though anxiety and the autonomic nervous system in the kidneys can give rise to an overactive bladder. Though kidney function is not directly connected to diarrhea and constipation, it is possible that decreased water intake can cause constipation. However taking slightly larger amounts of water and fluids will never cause diarrhea. Studies have reported that natural changes in the urinary tract may account for some of the apparent increase in lower urinary tract symptoms with increasing age. The sensation of bladder filling is reduced and bladder capacity falls, leading to an older person having less time to respond to the call to urinate and perhaps explaining why many older people complain of severe urge.