I have irritable bowel syndrome, most of the time i get mildly constipated, mild diarrhea on occasion. i'm also on valsartan, should i be worried about volume depletion from ibs?

Does not sound that your IBS is severe enough on the diarrhea side to cause clinically significant volume depletion, would worry about other causes for added on diarrhea , such as food poisoning or massive sweating, such as intense exercise or long exposure to hot temperatures that might create the premises for volume depletion if unable to keep up with hydration.

To avoid volume depletion, drink enough water daily so that your urine is mostly colorless. Wish you good health!