This condition is typically caused by air pockets in the line. The remedy is to let the faucets run briefly (for approximately 1 minute).
The air pockets create the white water; if you see discolored water - anything from brown to rust to yellow - do not use hot water! Just let the cold water run.
Discolored water is the result of iron content that was disturbed from the Water Main located in the middle of the road. Running hot water while water is discolored will pull the stirred iron content into your water heater and may cause significant damage to the unit.