Why? Because it is a huge shock to their warm running little bodies. I dont see it mentioned much if ever but I promise this has been one of the main mystery deaths of many a baby duckling. I have discussed this with lots of other waterfowl raisers and you will get little or no argument or debate on this issue. With breeding season in full swing for most of us this is something you should always keep in the back of your mind. I put out 5 gallon buckets of water so its lukewarm at least to get my drinking water for the ducklings instead of cold water coming directly from the tap. Dont know how my northern neighbors handle all their cold problems. My hats off to Yall! LOL! After they get about 2-3 weeks old it doesnt seem to be a problem. Hope this helps all yall and everyone has great success with their little quackers Shawn