The water tube is called winter tube or water bag. it is made from sheets of vinyl. The vinyl is slit and then sealed on all four ends. the water tube is generally 2’ wide and may be 8’ or 10’ in length. The water tube is made from 0.20mm, 0.25mm 0.33mm 0.42mm or 0.5mm Vinyl. There is a vinyl fill valve inserted in each bag to allow them to be filled with a garden hose. Once these water tube are filled, they are placed along the edge of the winter cover on in-ground pools to hold the cover in place