system
Given the following post, respond as if you're commenting on Reddit:
human
Why water?

The majority of all power plants uses some sort of energy source to heat up water. It is then the water vapor which turns the turbines that produces electricity.
Water is also a compound has an extremely high heat capacity (requires an incredible amount of energy to heat up).

**My question is this:** Why not use a compound which has a much lower heat capacity, and therefore requires a lower amount of burnt fuel to vaporize it?

Thank you!
gpt
There are many advantages to using water versus another substance in power plants: water is cheap, unreactive,non-combustible, easy to dispose, readily available, non-toxic, etc. There is no other substance that offers all of these beneficial properties.

Secondly, although water has a high heat capacity, this property isn't as detrimental as it may appear. When the steam condenses back to water after turning the turbines, it is pumped back into the system to be re-used. Thus, only a small amount of energy must be supplied to re-boil the water, and water's high heat capacity is irrelevant. Since the water also releases it's heat of vaporization when it condenses, this heat can also be partially recovered, as well. Therefore, using a substance with a lower heat capacity would not offer a significant advantage. The high heat capacity of water also helps keep the operating temperature of the system's fluids stable.