I've noticed that whenever I come in contact with running water (especially when I do my dishes), I have a desire to urinate. A quick Google search (link,link) gave me few different hypotheses:
Cold diuresis. Being in contact with cold water reduces temperature on the skin, which then constricts blood vessel to reduce heat loss, thereby increasing blood pressure and prompting the bladder to release excessive fluid.
Afferent innervation. I wasn't able to comprehend all the details of the process, but it seemed like this hypothesis is pertaining to the nervous system than circulatory system, hence different from first hypothesis.
Learnt psychological response. Second article linked above argues that this is a conditioned reaction, where even the sound of tap water triggers the desire to urinate. While it did not mentioned specific details of how this happens, I'm also assuming that this hypothesis is different from aforementioned hypotheses, because this hypothesis sounds more like a psychological response than biological reaction.
Which one of these hypotheses accounts for the desire to urinate when in contact with water? How exactly does it happen? If there is any other reason, feel free to add in the answer.