Check the listing for details. Water Blocks for In-Ground Swimming Pool Winter Cover (Various Kits Available). Condition: New. Listed at 18.98 USD. Aqua Blocks™ Helps Secure Winter Covers On Swimming Pools - (Choose Quantity) Aqua Blocks™ are an attractive way to keep your pool's winter cover in place all season long. The hard plastic construction offers a more durable solution when compared to vinyl water bags, which may rupture or leak. Aqua Blocks™ are easy to use. Simply place the Aqua Blocks™ around the edge of your pool cover, fill with water from your garden hose and snap on the top lid. In the spring, simply remove the lid and tip the Aqua Blocks™ over to drain. Note: Aqua Blocks™ are not designed for round swimming pools. Features: Made of high-density black polyethylene to survive the toughest winters UV inhibitor protects Aqua Blocks™ from fading & cracking Low profile and appealing shape to complement your pool Blocks easily nest into each other for easy storage Measurements: Inner dimensions: 36" L x 6" W x 4" H Warranty: 5 year limited warranty Approximate Blocks Needed by Pool Size: 12' x 20' Pool Size - (Qty 18) 12' x 24' Pool Size - (Qty 20) 14' x 28' Pool Size - (Qty 23) 16' x 24' Pool Size - (Qty 22) 16' x 32' Pool Size - (Qty 26) 16' x 36' Pool Size - (Qty 28) 16' x 40' Pool Size - (Qty 30) 18' x 36' Pool Size - (Qty 29) 18' x 40' Pool Size - (Qty 31) 20' x 40' Pool Size - (Qty 32) 25' x 45' Pool Size - (Qty 37) 25' x 50' Pool Size - (Qty 40) 30' x 50' Pool Size - (Qty 42) 30' x 60' Pool Size - (Qty 45)