The reason it takes a lot of heat to change the temperature of water, or to cause a phase change from solid to liquid, or from liquid to gas, isn't because "water is a poor conductor of heat," but rather because "water has a high specific heat," which is the amount of energy (calories, BTUs, etc) needed to change a given weight of the material (one gram) by a given amount (one degree celsius).

This is what makes water pretty much the "ideal material" to use to transmit power in things like steam engines (turbine steam engines are still heavily used in power generation) or to carry heat in things like engine cooling systems or residential/commercial heating systems.

Water really has quite a few remarkable properties from a scientific or engineering standpoint.