The answers are: 1) It Depends and 2) We Don’t Have Accurate Data.
Electric power generation is the biggest user of water in the US (with agriculture being a close 2nd). How water is used is very complex and data are not very accurate. The amount of water any given locale uses to produce electricity depends primarily on the type of fuel used and the type of power generating technology used. There are great variations: wind technology uses little water and biodiesel-fueled power plants use lots (soybeans need water).
An NREL (National Renewable Energy Laboratory) study from 2011 concluded that water withdrawal and consumption data are not very accurate. In their words:
“Accurate estimates of water use in individual power plants, and the effect of this water use on a regional scale, will be elusive until more studies are conducted for the variety of technologies and cooling systems currently in operation along with those expected to be developed and deployed. Furthermore, calibration of these values on national and regional scales will remain challenging until methods for collecting and evaluating data by federal agencies has improved.”
The NREL study is concerned about promoting power generating technologies that use less carbon but may require more water. They are interested in balancing the need to conserve water and use less carbon.
While an IEEE document states that 95 liters of water are used on average to produce 1 kilowatt-Hour of electricity, they do not show how that number was calculated. Their charts of water usage by type of fuel and by type of power generation technology are helpful but we are not told how — exactly — they add up to 95 liters water/1 kWh. Their charts exclude renewable technologies, such as wind and solar.
The US Energy Information Administration, EIA, tells us that:
In 2011, the average annual electricity consumption for a U.S. residential utility customer was 11,280 kWh, an average of 940 kilowatthours (kWh) per month. Louisiana had the highest annual consumption at 16,176 kWh and Maine the lowest at 6,252 kWh.