A backyard swimming pool can be a great deal of fun for family and friends, but one thing to be aware of is how much water pools require. An average size in-ground swimming pool needs about 20,000 gallons. Even above ground pools require a lot of water. A 15 foot diameter aboveground pool needs 5000 gallons, and that's far from the largest size available. It is important to be aware of possible water fees, before you incur them.
Thankfully, swimming pools don't need to be emptied very often, but during the initial filling, you could rack up some hefty water fees (hundreds of dollars, depending on where you live). Fortunately, there are some things you can do to avoid high fees.
First, you'll want to check with your municipality as fees for large scale water usage can vary greatly from town to town. Before you simply turn on the hose and let it run, ask your local branch if there are any discounts available for swimming pool owners.
Some communities charge separately for water usage and sewer usage (water disposal). One thing you can do to avoid being double charged is install a diversion meter in the plumbing supply system (make sure your community allows this). Diversion meters measure your water usage and waste drainage separately and help ensure you are only charged once. Installation costs for these meters are often less than water disposal fees, so it can be a worthwhile addition.
Remember, once you have your swimming pool filled, you should use a pool cover in order to reduce evaporation that could require adding water on a daily basis.
Source: Sunset's Swimming Pools and Spas