13.1: Introduction
Water infrastructure is intended to provide water for a variety of uses, to remove and treat wastewater, to provide flood risk mitigation, to aid water navigation, to provide recreational opportunities and to generate electricity or power. Water is essential for human life, with humans comprised of roughly 50-70% water and drinking (or ingesting) roughly 2 liters of water per day. Droughts and agricultural salt incursion due to inadequate water management are often cited as significant causes for the failure of historic civilizations.
Anthropogenic water withdrawals in the United States are shown in Figure 13.1.1 in billions of gallons per day. Irrigation for agriculture and thermoelectric power are the two largest uses, and both of these uses have corresponding large wastewater runoffs. With public water supply at 50 billion gallons per day and a population of 300 million, per capita water use is roughly 50,000/300 = 170 gal/day (640 liters/day) which would include commercial uses, drinking water, fire fighting, washing, watering, etc. Note that Figure 13.1.1 does not include withdrawals for eco-system uses other than agricultural irrigation.
Water withdrawals are different from water consumption or use. Withdrawals for uses such as thermoelectric power are often returned directly to their source, although at a higher temperature. Similarly, public water supplies may be used, treated as wastewater, and returned to a river. Thus, water may be re-used and withdrawn numerous times.
Access to safe and sustainable drinking water and sanitary resources are major problems in many areas. The United Nations estimates one billion people lack access to safe drinking water and 3.5 billion people lacking access to sanitary facilities (WWAP, 2016). A Millennium Goal is to reduce the number of people without access to safe water in half by 2015.
Water transportation is a significant mode for freight traffic. Figure 13.1.2 shows inland waterway freight flows in the United States. The importance of the Mississippi water system and the Great Lakes are evident.