It is a scorching hot day in Beanotown. Walter and his friends are enjoying themselves in Walter's new swimming pool, but Dennis and his friends cannot join in. Sergeant Slipper comes past and tells them that they cannot play with water today because there is a water shortage. Hot and wanting their own pool, Dennis and his friends decide to dig one in Dennis's backyard and figure out how to fill it later. Their digging leads them to find the old drains of Beanotown. In their exploration and hunt for water, they end up being chased by Slipper, and releasing the overflow of Beanotown Lake. The water flows right through the drains and fills the hole in Dennis's garden, giving the boys the swimming pool they wanted.