The opening is almost 6 inches wide. The bladder is 14 inches long. The water bladder top folds over itself and then you slide a plastic sealing clip to seal the bladder. I have medium/large hand and can get my hand inside the bladder without any problem. I usually wipe it down and then use a hair dryer on low and blow dry it for a few minutes to prevent any potential mildew or odor build up.