Water hoses supply approximately 5 to 10 gallons per minute in a normal city setting. In a rural setting this may be substantially lower if the water comes from a well and pump. After an hour of constant water flow, you'll end up with 300 to 600 gallons of water.
At an average of 300 to 600 gallons of water per hour, it will take between 15 and 30 hours to fill a small inground pool. A small inground pool at 12 feet wide and 24 feet long with an average depth of 7 1/2 feet holds 8,900 gallons. Average-sized swimming pools hold up to 25,000 gallons of water.
Water trucks can fill a pool much faster than a standard hose. A 25,000-gallon pool will take from 42 to 84 hours to fill using a garden hose, based on normal water delivery. Water trucks deliver swimming pool water in a few trips as some trucks carry up to 4,000 gallons of water. Contact your water utility service to find out if there are special rates for filling swimming pools and compare them to water truck delivery services.