Water is unique because it reaches its smallest volume/highest density at 4 degrees C, so technically it compresses (contracts is prolly a better word) as it warms or cools to that point even without changing pressure. And expands as it moves away from that point. It's a very small amount and if contained, that small amount can exert an astounding amount of pressure. That's why we have expansion joints/tanks on our water heaters. And also why, for the most part, it's considered incompressible.
Once it reaches 0 degrees all hell breaks loose. All this is a good thing, since otherwise our oceans would freeze from the bottom making it much more difficult for life to take hold.
Now you're gonna start calling me Prime9.
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