When a water line freezes, the pressure inside can increase significantly, sometimes reaching thousands of pounds per square inch (PSI), due to the expansion of water as it turns to ice (which expands by about 9%), potentially causing the pipe to burst if the pressure becomes too high; a typical household water line might see pressure jump from around 60 PSI to over 200 PSI when frozen. 

Key points about freezing water pressure:

Expansion factor:

Water expands by approximately 9% when it freezes, creating significant pressure buildup in a closed pipe system. 

Potential for damage:

This pressure can easily exceed the capacity of most household water pipes, leading to bursts and water damage. 

Pressure variation:

The exact pressure increase depends on the size of the pipe, the amount of water trapped within the ice blockage, and the existing water pressure in the line