Though water freezes at 32º Fahrenheit, pipes act as a barrier—the water inside them generally doesn't freeze until it is below 20º F. Pipes with little or no insulation could freeze when the outside temperature dips under 20º F. Water expands as it freezes, which is troublesome for pipes. As the water freezes along the pipe's length, pressure increases between the ice and a closed endpoint, such as a faucet or washing machine hose. The pressure grows too large for the limited space to handle, which results in a pipe bursting.