Whether you are filling your pool for the first time or refilling your pool, we usually recommend filling your swimming pool with water using a garden hose. Just make sure there are no sharp edges on the hose end that could damage your swimming pool liner.
Place the end of the hose on the bottom of the hopper (the deep end of your pool), turn the water on, and fill pool with water. As the pool is filling with water you may need to smooth out any wrinkles in the liner, before 2 inches of water covers them. Once wrinkles are covered they will be impossible to remove.
Note it may take several hours to fill and use quite a large number of gallons of water. If you are using city water you will likely see a large spike in your water bill.
High Pressure Water Source
If you are filling your pool with a fire hydrant, water delivery via tanker truck or any other high pressure source of water, you will still need to fill the hopper of the pool with 2 inches of water from a garden hose before the high pressure source is turned on.
Make sure to direct the water from the high pressure source into the partially filled hopper. If the high pressure source of water is allowed to hit the hopper sides or bottom directly it can make impressions in the freshly troweled vermiculite under the liner and disturb the otherwise smooth pool area.