You see a solid that looks like an ice cube, but it doesn't melt at room temperature. Could the solid be frozen water?

A solid that doesn't melt at room temperature can't be water. The freezing point of pure water is 0ºC at normal atmospheric pressure. Room temperature is 20-25ºC.

The attached phase diagram shows you how water's freezing temperature varies with pressure. The phase transition from solid to liquid will occur at combinations of temperature and pressure that fall on the solid-liquid boundary line. As pressure decreases the boiling point of water increases, but not much. The...

A solid that doesn't melt at room temperature can't be water. The freezing point of pure water is 0ºC at normal atmospheric pressure. Room temperature is 20-25ºC.

The attached phase diagram shows you how water's freezing temperature varies with pressure. The phase transition from solid to liquid will occur at combinations of temperature and pressure that fall on the solid-liquid boundary line. As pressure decreases the boiling point of water increases, but not much. The maximum freezing temperture is 0.01ºC at a pressure of 0.006 atm, which is its triple point. The triple point of a substance is the temperatue and pressure at which solid, liquid and gas exist in equilibrium. At conditions below the triple point solid water undergoes sublimation to gas.