The reference freeze/boil points, water's densest temperature, and why ice and steam each take up more room.
Freezing and boiling points
At normal atmospheric pressure, plain water freezes at about 0 °C and boils at about 100 °C. These two points are the standard reference temperatures used throughout plumbing and heating work, from frost protection to hot water safety.
Water is densest at about 4 °C
Unlike most liquids, water does not simply keep shrinking as it cools. It contracts steadily down to about 4 °C, where it reaches its maximum density, then expands slightly again as it cools further towards freezing. That is why the coldest water in a pond sits near the surface while slightly warmer, denser water stays lower down.
Ice takes up more room than water
Water expands as it freezes: ice is roughly 9% less dense than liquid water, which is why ice floats. That same expansion is what can split a pipe or push a joint apart when water freezes solid inside it — the failure often only shows up as a leak once the ice thaws.
Steam takes up far more room than water
Boiling is a change of state, not just a temperature rise: the liquid turns into a gas that is far less dense, so the same mass of water takes up a much bigger volume as steam. The mass does not change, only how much space it fills, which is part of why an uncontrolled steam release is so dangerous.