We usually recommend filling your swimming pool with water using a garden hose. Make sure there are no sharp edges on the hose end that could damage your swimming pool liner. You will place the end of the hose on the bottom of the hopper. 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.
If you are filling your pool with a fire hydrant, 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 trowled vermiculite under the liner and disturb the otherwise smooth pool area.