This month's question asks why the water looks milky during the cold winter months. The article discusses several reasons for this condition: water density is greater in cold weather, causing slower chemical reactions which make it difficult to get floc to settle; or, floc carrying through the filter as particulate floc. Adjusting pH in response to seasonal temperature variations, using ferric salts for coagulation during the winter months, jar testing, and temperature changes in cold water causing air binding in the filter are all discussed.