How Many Gallons of Water Does a 20 by 40 Feet Pool Hold?

A 20-by-40-feet pool with a 7-feet average depth holds 41,900 gallons, and a pool with an 8-feet average depth holds 47,900 gallons. To keep a pool filter working properly, it is important to keep the proper amount of water in the pool. The water level should reach the midpoint on the tile backsplash, or it should rise above the skimmer opening. Water often must be added to the pool periodically throughout the season.