Monday, September 26, 2011

Water is Our Story

The United States is a “first world” economy with what I thought were established water use patterns until I reviewed the data. The US Geological Survey has conducted water-use compilations every 5 years since 1950. Water use per capita and total water use peaked around 1975-1980 (between two US Geological water use estimates) when growing recognition of the limitation of water as resource and regulation began driving water conservation efforts. At the time, US population was around 225 million. Despite the population growing almost 38% to 310 million water use appears to have leveled off, but since 1995 has begun to climb again after the gains from conservation can no longer make up to the increasing population.

Cooling water for thermoelectric power generation has accounted for the largest water withdrawals since 1965, and in 2005 accounted for 49% of total withdrawals. Thermoelectric water withdrawals are non-consumptive, the water is returned to the water source after use. Thermoelectric-power water withdrawals have been affected by limited water availability in some areas of the United States, and also by sections of the Clean Water Act that regulate cooling system thermal discharges. Since 1972, power plants have increasingly been built or converted to using wet recirculating cooling systems or dry recirculating (air-cooled) systems instead of using once-through cooling systems. Hydroelectric power is not counted as a water withdrawal because the water does not leave the river or other water reservoir.

Irrigation accounted for 31% of total water withdrawals and 61% of the total water use excluding thermoelectric. During 1950, 77% of all irrigation was from surface water, primarily in the Western States. By 1980, the quantity of groundwater used for irrigation had nearly doubled, and groundwater accounted for 40% of total irrigation withdrawals. In 2005, 42% of irrigation withdrawals were from groundwater. The total number of acres irrigated increased from 1950 to 2005, though the water used in irrigation has not increased by as much. In 2005, the total number of acres irrigated was 60 million acres. More efficient methods of irrigation are gradually being adopted.

Water use for public supply has increased continually since 1950, along with the population served by public supply. Public-supply water use in 2005 was about 11% of total withdrawals and 21% of all freshwater uses excluding thermoelectric power generation. The percentage of groundwater used for public supply increased from 26% in 1950 to 33% in 2005. Estimated withdrawals for self-supplied domestic use (rural private drinking water wells) increased by 82% between 1950 and 2005. Private water well supplied 57.5 million people in 1950, or 38% of the total population. In 2005, private drinking water well supplied 42.9 million people, about 14% of the population. This would translate to an increase in per capita use from less than 40 to almost 90 gallons per day.

The final category of use, “other” includes industrial, mining, commercial and a relatively new category, aquaculture. This little category which today accounts for 7.6% of total water withdrawals and 14.8% of water use excluding thermoelectric power tells the story of our nation in terms of regulation and economy. In 1950 26% of the consumptive water use was in this category, today it is 14.8% with over a quarter of that amount going to aquaculture. Total water use in this category had fallen in absolute terms since 1950 (after peaking in 1970) and is generally attributed to significant declines in production and employment in: primary metal manufacturing, paper manufacturing, chemical manufacturing and petroleum and coal products manufacturing. Overall, manufacturing employment in the United States declined 19% since 1990 and probably reflects an absolute economic decline in the sector. Our water use tells the story of our nation. We are no longer an industrial manufacturing economy.

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