While the greenhouse gas emission reductions of switching from coal to natural gas have been well documented, less attention has been paid to their effects on water. Worldwatch Sustainable Energy Fellow Saya Kitasei and I recently coauthored a briefing paper comparing the lifecycle impacts of natural gas-fired and coal-fired electricity on fresh water in the United States. We looked at water consumption from mining and drilling in a few different resource basins, including regions where natural gas is produced by more water intensive methods like hydraulic fracturing or coal seam dewatering. We also looked at water consumption in processing, transportation, and at the power plant itself, along with pollution controls and waste disposal for those sites.
Perhaps unsurprisingly, we concluded that the biggest consumptive use of water comes at power plants, where water is routinely used as a coolant. Natural gas-fired power plants generally use less water for cooling for two major reasons. First, natural gas-fired power plants are often more efficient than coal-fired power plants, so less heat needs to be dissipated. Second, natural gas can be burned directly in a turbine (unlike coal, which is solid), and gas turbines are air-cooled. So power plants running gas turbines (including combined cycle plants, which run natural gas through a gas turbine, then use the waste heat to boil water and run a steam turbine) use less water for cooling than plants with steam turbines.