I googled gaining 5-10 pounds in a day, because that seemed a bit much in one day to me. I know when my father had congestive heart failure, he had to weigh himself every day and report such high amounts gained in a 24 hour period. Here's what I found: https://www.shape.com/lifestyle/mind-and-body/when-your-weight-fluctuates-whats-normal-and-whats-not