Three things about water affect almost all of cooking. First are the hydrogen bonds, which is why it has an incredibly high boiling point. Another is that it's a polar molecule, so that it dissolves a lot of things, and there are things that won't mix with it. And then there's how much energy it takes to heat water.
Pressure cookers are relatively inexpensive, they're in every kitchen store, your grandma probably had one, but a lot of people don't. A pressure cooker is interesting because by pressurizing the vessel, you're able to cook much hotter than the boiling point of water, and still have water be present.
The physics of water is central to cooking, because food is mostly water. All steak that you cook is actually boiled on the inside.
