Why are you carrying a bag of water?

Today I met my brother and his family for a day's shopping and a bite to eat. Simple enough plan isn't it? What could possible go wrong? The answer being that the plan involved me and therefore, anything. 

In one shop, my sister in law had a lot to achieve. My brother and I whiled away the time loitering. And dripping water onto the floor. This is because a bottle of water had spilt over in my bag - at first unbeknownst to me and then progressively more embarrassingly known to me as it turned into a pool. Eventually a shop assistant came over with a cloth to wipe it up and gave me an unmistakable look of 'why the fuck are you carrying a bag of water'. To which I had no appropriate response, life and experience not having provided me with one to date.