70% of the earth’s surface is water. Humans, animals, and plants need clean water to stay healthy. Water conservation is necessary because of a limited amount of fresh water, inefficiency in water use, and the need for water in almost every human process.
Though it varies by country, the world uses most of its water for irrigation. Within the categories of residential, industrial, and irrigation use, fresh water goes to drinking, agricultural processes, and power production.
Most people can live only a week without water. Out of all earth’s water, 97% of it is salty, ocean water. People get drinking water from wells (groundwater) or surface water (lakes & rivers). In the U.S. only about 11% of usable water is used for public consumption.
The water is then treated or stored in reservoirs or storage tanks. Some people get water from the sea (see “Extracting drinking water from the ocean” below).
Most usable water comes from underground. State or local governments enforce standards for well construction and use. A is be dug or driven (see drawing below), but most modern wells are drilled. Wells can be over 1,000 feet deep and usually include treatment and a pump to transfer clean water to your faucet.
Crops and livestock need water for growth. Irrigation accounts for 70% of the world’s fresh water use. 3 Some common products in the U.S. and the water it takes to produce them include:
Industry & Powerplants
Industry and electric power plants withdrew 53% of U.S. fresh water in 2000. (See chart below). Electric power plants use most of the withdrawal for cooling. Industry uses water for products such as:
Steel: Producing one ton of steel takes about 62,600 gallons of water.
Automobiles: Manufacturing a new car takes about 39,090 gallons of water.
Soft Drinks: The U.S. soft drink industry uses 12 million gallons of water annually.
Large dams worldwide have increased from 5,000 to 45,000 since 1950. Hydropower provides 7% of U.S. energy. It is the leading source of renewable energy and generates limited pollution. Dam operators release water according to electricity needs. The water flows through turbines, causing them to rotate and generate electricity.
See Energy for more information.
In China, the recently constructed Three Gorges Dam, is the largest dam in the world. It harnesses the power of the Yangzi River and produces the energy of 18 nuclear power plants. However, the 395 square mile reservoir displaced 1.2 million people and change forever the waterway’s ecosystem. Reservoirs created by dams also increase evaporation, resulting in a loss of fresh, usable water.
Comparing poor & wealthy countries
Poor countries lack access to drinking water or must pay a higher price for it. One study comparing Washington D.C. and a slum in Guatemala City showed a huge price gap. The average household in Washington D.C. pays about $350 for a year’s supply of water (127,400 gallons). The same amount of water would cost over $1,700 in Guatemala City. Poor residents in El Salvador and Jamaica spend 10% of income on water. Those in Uganda spend 22% of income on water.
Government subsidies often only help higher income families. Residents in urban slums of developing countries lack access to municipalities and must purchase water from private vendors who often raise prices unfairly. For example, residents in several Asian countries pay 10 times as much for private water than do middle-income residents supplied by municipalities.
Future water availability
The UN predicts 70% withdrawal of run off water by 2025 (up from 54% in 2003). The UN also predicts that over 65% of people worldwide will live in regions of high water stress by 2025 (up from 40% in 2003).
Scientists predict that global climate change will affect future water availability in the following ways :
- Changes in precipitation patterns may increase drought.
- Temperature increases will lead to more rain than snow.
- Temperature increases will lead to a shorter season of snow pack (a natural reservoir of fresh water).
- Flooding will increase in the winter, decreasing river flows in spring and summer.
- Sea level rise will decrease fresh water supplies for coastal regions.
For more information, see Global Warming
The price of water also depends on availability. For example, Australia’s water prices increased 20 fold from December 2006 to 2007, partly due to drought. In some countries, selling water is more profitable than using it to grow crops, but as farmers pump out more water to sell, underground aquifers drop rapidly. Along with aquifers, lakes and rivers are drying up around the world. Rivers reduce to a trickle during dry season, including major rivers such as China’s Yangzi and Yellow Rivers, India’s Ganges River, and Egypt’s Nile River. Africa has had major droughts in every decade for the last 30 years. Drought took one million lives in Ethiopia in 1984.
U.S. public water utilities process about 38 billion gallons of water every day. Water plants treat water for drinking before it reaches our faucets. They also treat water after we use it, for the safety of lakes, rivers, and aquifers that receive it.
Municipalities process water for drinking in about 9 steps:
- Screening. Remove floating objects.
- Aeration. Dissolve oxygen in the water to remove smells and tastes, promote helpful bacteria, and remove metals (in solid form) from solution.
- pH correction. Make water acidic for easier metal removal and coagulation (forming particles in one mass for easy removal).
- Coagulation & Flocculation. Add substance to trap impurities which settle at the bottom or float as suds.
- Sedimentation. Drain water, remove impurities from top or bottom.
- Pre-chlorination or de-chlorination. Chlorine adjustment kills harmful algae & bacteria.
- Filtration. Water flows through sand to reduce life forms such as bacteria & viruses.
- Disinfection. Chlorine, ammonia, or ozone treatment kills remaining life forms. Leave in residual disinfectant to prevent re-infection.
- pH adjustment. Add calcium carbonate (lime) if too acidic. Desired pH: 6.5 -8.5
Advanced techniques include microfiltration, reverse osmosis and ultraviolet disinfecting.
Contaminants to treat in water include:
Sewage & Reclamation
Septic drain fields or leach fields filter wastewater with underground soil. Sewage plants operate with a different method, treating wastewater for:
- Nutrients & organic matter
- Inorganic matter
- Heavy metals
- Hazardous waste
Sewage plants treat wastewater in three basic steps:
1. Remove solids by screening and settling in sediment tank.
2. Removed dissolved contaminants with:
- Sludge beds, trickling filters
- Skimming contaminants off the top
3. Remove nutrients using:
- Carbon filters
- Chemicals that cause nutrients to solidify and float or sink
- Reverse Osmosis (pumping solution at a high pressure through a filtering screen)
Though the effluent, or resulting water is clean, it’s not potable. However, operators of parks and golf courses may use it to irrigate. Some homes have reclaimed or graywater systems that gather and treat water from sinks, showers, and washing machines for re-use on lawns and gardens.
Over the past 30 or so years, many municipalities and water districts in the U.S. have campaigned vigorously to reduce the amount of contaminants entering the water system through education, monitoring and charging additional fees to commercial and industrial users for disposing of heavily contaminated waste water. In many cases, the cost for waste water disposal is higher than for incoming fresh water.
For more on the environmental effects of sewage, see Pollution
Treatment in developing countries
1.3 billion people worldwide do not have clean drinking water. Countries lacking huge water treatment plants use similar, but simpler methods than large municipalities :
- Waste stabilization ponds & wastewater storage and treatment reservoirs are shallow basins made to retain and treat wastewater for several days.
- Constructed wetlands are man made ponds containing wetland plants like reeds and bulrushes. Sewage flows through the soil, allowing microorganisms to break down organic material.
- Chemically enhanced primary treatment is the use of chemicals like metal salts or polymers to help suspended particles, organic matter, and nutrients clump together for removal.
- Upflow anaerobic sludge blanket reactors are tanks filled with wastewater from the bottom. The tanks contain sludge with microorganisms that cause waste to sink. The process produces gases that cause the wastewater to mix, and the cleaner fluid floats to the top.
Worldwide water prices have been steadily increasing. In a 2007 survey of 14 countries, average municipal prices ranged from $.66 to $2.25 per cubic meter.
Cost of freshwater & infrastructure
In 2008, the average U.S. individual pays $.25 for water per day. Water systems in the U.S. cost $3.5 billion a year. The major cost involved is that for pumping water which depends largely on the distance transported. For example, Mexico City must pump its water 1,000 meters to reach its high elevation, which costs hundreds of millions of dollars annually. Costs also depend on the water supplier, with a wide range between subsidized municipalities and private vendors. Desalinated water costs over $1,000 per acre-foot, compared to normal sources at about $200 per acre-foot. However, desalinaton costs are steadily dropping as technology improves.
To withdraw water from a natural source, one must obtain water rights. “Riparian Law,” used in the U.K. and Eastern U.S. allows water withdrawals for those who own land next to rivers. Another law, known as “priority appropriations,” gives senior water rights to the oldest holder, independent of owning land next to a river. Utilities withdraw and store water based on water laws of the nation or regional system. Customers usually obtain water from the utility with a specific contract. For example, the contract may only allow irrigation on certain lands. Each region uses a variation of these laws. There are fewer groundwater pumping laws that are poorly enforced.
California is a complex example of the importance of water rights. California’s water dilemma is that 75% of its precipitation falls in the north, while 75% of its population lives in the dry south. Southern California uses water transported in aqueducts from Northern California and water piped from the Colorado River. In 1922, California made a compact with seven surrounding states about withdrawing water from the Colorado River. The Supreme Court approved the compact that allowed California more withdrawal due to its rapid population growth. The compact allocated more river water than was available since planners used data from wet years. It also ignored Mexico, the final potential harvester of Colorado River water.
Farmers down stream from Beijing on the Juma River found low water flows in 2004. A state-owned petrochemical plant had begun withdrawing from the river at a newly built dam. The farmers protested without success. 120,000 villagers are currently struggling to make a living from farming. Industries claim water rights in similar situations throughout the world.
Dropping water tables
The average residence in U.S. uses over 100,000 gallons of water inside and outside, putting pressure on water sources like aquifers. Groundwater levels rise and fall based on the following:
- Variations in rainfall
- Amount of pumping
As people pump out more and more groundwater, ground level lowers with the water table. This result, known as Land Subsidence, occurs in nearly every state in the U.S. For example, in San Joaquin Valley, California about 30 feet of land subsidence occurred between 1925 to 1977.
Land subsidence may permanently reduce an aquifer’s ability to store water. Over pumping coastal groundwater increases the chance of coastal flooding and saltwater intrusion; the seepage of ocean water into groundwater. Saltwater intrusion contaminates drinking and irrigation water. Besides loss of groundwater, land subsidence damages the following:
Desertification is when land becomes depleted of nutrients and moisture, unable to support life. These dried up lands are in half of the world’s countries, covering 1/3 of the earth’s surface. Some causes include:
- Climate variations and drought
- Over pumping
- Over cultivation
Dried out land affects people and their environment in the following ways:
- Diminished food production from declining soil productivity
- Increased flooding
- Reduced water quality
- Increased sedimentation in rivers and lakes
- Health problems from dust
- Loss of livelihood, forcing people to migrate
Development, pollution, introduced species, and over pumping damages water ecosystems like oceans, lakes, rivers, and estuaries. Over fishing and other exploitation reduces populations or drives species to extinction, which threatens the 200 million people that depend on fisheries for their livelihood. Dams destroy habitat and species by reducing river flows. They alter whole ecosystems by creating huge, unnatural lakes, and by blocking fish from downstream.
Man made chemicals or natural materials released by human activities pollute groundwater, surface water, and ocean water, disrupting ecosystems and damaging human health. 1.3 billion people worldwide do not have clean drinking water. See our Pollution Page for more information, including drinking water contaminants.
Floods & Droughts
Droughts occur when precipitation is lower than normal for a prolonged period of time. Floods occur based on the following reasons:
- Intensity of rainfall
- Duration of rainfall
- Soil conditions (dry vs. absorbent)
- Ground cover (cement vs. vegetation)
Other water related natural disasters claim human lives by the thousands. The Indian Ocean Tsunami of 2004 killed over 250,000 people in 12 countries. Over 1,000 people died in U.S. Gulf Coast hurricanes in 2005.
Global water demand has tripled over the last 50 years. Desalination, using less water for agriculture, and rationing water are a few methods of responsible water use.
Extracting drinking water from the ocean
As rivers dry up and aquifers recede, countries turn to the largest source of earth’s water; the ocean. Removing minerals, such as salt, from seawater to produce clean water is called desalination. There are about 7,500 desalination plants worldwide, with 60% in the Middle East. Plants in the Americas are limited because desalination costs more than other methods of getting clean water.
To separate water from minerals, plant workers use Reverse Osmosis or Distillation. Reverse Osmosis is pumping seawater at a high pressure through a screen to filter out minerals. Distillation begins with heating seawater until it steams. The steam is pure water and minerals are left behind. Desalination plants can recover about 15-50% of seawater. Some negative effects of desalination include:
- High maintenance & cleaning before and after treatment
- An energy intensive process (especially distillation)
- High salt concentrated discharge
- Chemical & toxic metal discharge
Growing more food with less water
As farmers over pump aquifers, the water table drops and drillers must dig deeper wells. Deeper wells require more energy to pump water out. This drop has caused a decline in China’s rice and wheat production by millions of tons since 1997. Due to water shortages and aquifer depletion, Israel has completely banned irrigation for wheat. Countries with severe water shortages import grain since producing it requires expensive water. For example, Israel imports 40% of total grain, and Algeria, over 50%.
Since the world uses most water for irrigation, and populations are growing while water supplies are shrinking, countries need to grow crops that are less water-intensive. They must produce “more crop for every drop.” Agricultural scientists are working on water saving methods. For example, farmers can reduce water us in rice production with these methods:
- Grow denser crops to reduce evaporation
- Reduce water use in land preparation
- Use direct seeding instead of transplanting
- Reduce seepage and percolation
- Change the growing schedule to increase rainfall use
- Use rotational water distribution instead of continuous flow
- Reuse water
Water economists suggest charging one set fee for a given amount of water, and extra fees for high volume users. This ensures water for poor communities and encourages efficient water use. Some countries reduce demand by rationing all amounts of water. For example, Jordan limits water use in the city of Amman to three days per week. In Damascus, the government allows water use less than 12 hours per day.
Intel Corporation recycled 75% of water used for manufacturing by reusing 530 million gallons of water within the plant in 2007. The corporation also manages 825 million gallons of wastewater instead of sending it to the city’s wastewater plant. They also treat 575 million gallons of wastewater and return it to the local underground aquifer.
MIT, a private university in Cambridge, Massachusetts, reduced campus water consumption by 60% from 1997 to 2005. By installing low flow appliances and a non-potable waste water re-use system, MIT saves millions of gallons every year. MIT changed their cooling and laboratory systems with several programs with a payback time of about two years.