Have Plan B activities up your sleeve in case of bad weather. These could include a movie, indoor games and even some water activities, like apple bobbing or fishing for magnetic fish in a bowl, etc. If you plan some non-pool games that can be played anywhere, you'll be covered for activities should the weather turn bad. If you're having a barbecue, shift under the cover of a back porch and the guests can take the food indoors and eat as they watch a movie or chat.