Cause never found none of usual suspects eg drink , gall stones etc right down to do I keep scorpians as pets . Most likely cause was an infection of some kind . After a lot of digging on internet found legionaires can cause pancreatitis and we had just had the hottest few weeks of the year , so in my book that was the most likely cause . So now in summer what I don't use in a few days is dumped this time of year is ok not enough heat to be a problem . If rainwater harvesting do you empty tank every few days or is there a bit left in bottom that could be a breading ground for nasties