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Water is unique among human necessities in the enormous quantities used - mainly for agriculture. For example, California uses 35 million acre-feet per year, i.e. a bit more than an acre-foot for each of its 30 million inhabitants. Because of this quantity, the main cost of water is transporting it. Oil can be imported profitably to the U.S. from the Persian Gulf, but moving water is costly. (Note that an acre-foot (an acre covered a foot deep) is about 7,755 barrels or 1233 cubic meters, and the price for an acre-foot of agricultural water is only a few times the price of a barrel of oil).

2004 update: The current estimate for California is 43 million acre-feet per year including agriculture. Sizes by John Lord published in 1995 says

At current American rates of consumption, on average one acre-foot of water is enough to meet the industrial and municipal needs of four people for a year.
There have been proposals to desalinate sea water in places that run short. According to the Britannica article on desalination, about 8 million cubic meters of desalinated water is produced per day, mostly in the Arabian Peninsula. This amounts to 2.4 million acre-feet per year. We could use desalinated water in California if we had to, but we probably wouldn't use it to grow alfalfa. See desalination further down on this page.

This page is still under construction. There is more to come. I had thought I had a lot more work to do in order to collect the facts to show that water supply is not going to limit human population to a level below 15 billion. However, the article America's Water Supply: Status and Prospects for the Future by Kenneth D. Frederick covers much of the required ground better than I could for the United States. The article is from the on-line magazine Consequences: The Nature and Implications of Environmental Change.

The last paragraph of the article reads

In summary, with improved basin-wide management of supplies, institutions that enable water to be transferred efficiently and expeditiously among uses in response to changing supply and demand conditions, and cost-effective approaches to protecting aquatic ecosystems and drinking water supplies, reliable supplies of freshwater will be available at readily affordable prices for the foreseeable future.

Here's another important paragraph.

Growing water scarcity in the arid and semiarid West has fostered a number of bold proposals to utilize the enormous quantities of water stored in polar ice or to divert northern rivers in the largely uninhabited areas of Canada and Alaska. However, the technical, economic, legal, and environmental obstacles to transporting and using icebergs to supplement water supplies in an area such as southern California currently appear insurmountable. The enormous financial and environmental costs of proposals such as the North American Water and Power Alliance that would transport 110 million acre-feet of water annually (about eight times the average annual flow of the Colorado River) from Alaska and northern Canada to the western United States and northern Mexico have relegated them to the realm of science fiction for the foreseeable future.

Here I draw an almost opposite conclusion.

We won't need any such grand projects for the forseeable future, but when and if our descendants need enormous increases in water supply, they can get them, perhaps at expense comparable in relation to per capita GDP to the expense our immediate ancestors spent on water projects. Probably the expense in proportion to the GDP of the region benefitted will not be as great as the 1904 Owens Valley aqueduct was in proportion to the GDP of Los Angeles at the time.

At that time, the population of Los Angeles was 200,000 and the per capita income for the U.S. was $1100. The cost of the project was $23 million. Therefore, it corresponded to 1/10 th of a year's income for the inhabitants of the area. 1/10 th of a year's GDP for the U.S. would come to $800 billion. It doesn't look like we will have to spend that much for increased water supply in the near future, but we'll do it if we have to. I'd do a more specific calculation if I knew the size of the population in the area proposed to be served by the North American Water and Power alliance (9).

Around 1900 people thought in large terms. Recently, it has become fashionable to think small.

However, the main reason why large American projects for agricultural water are unlikely to be undertaken soon is that American agriculture produces surpluses beyond what can be sold at present - and is predicted to do so for a long time. Agriculture using the area supplied by wells in the Oglallala Aquifer might have to be abandoned when it runs dry until the demand for agricultural goods increases enough to justify the expense of increased water supply. Needless to say, this will be painful for the people presently using Oglallala water for farming. They will have to get other jobs.

The complex history of water supply has produced pricing anomalies that are only now being overcome. Large past multi-use projects (water supply, electricity, flood control, recreation) had the costs allocated by politics and the resulting water supply divided up by politics. The result was that certain farmers were allocated very cheap water on a use-it-or-lose-it basis. They were not allowed to sell their allotments to cities, and sometimes this resulted in cities paying tens of times the price for water as was paid by farmers in the same area. Preferences for farms of 160 acres or less further complicated the picture.

Here are some facts from the on-line Britannica Encyclopedia.

The area that can be irrigated by a water supply depends on the weather, the type of crop grown, and the soil. Numerous methods have been developed to evaluate these factors and predict average annual volume of rainfall needed. Some representative annual amounts of rainfall needed for cropland in the western United States are 12 to 30 inches (305 to 760 millimetres) for grain and 24 to 60 inches (610 to 1,525 millimetres) for forage. In the Near East, cotton needs about 36 inches (915 millimetres), whereas rice may require two to three times that amount. In humid regions of the United States, where irrigation supplements rainfall, grain crops may require six to nine inches (150 to 230 millimetres) of water. In addition to satisfying the needs of the crop, allowances must be made for water lost directly to evaporation and during transport to the fields.

Only a tiny fraction of these amounts of water end up in the plants. Therefore, there is an enormous potential for growing the plants using very much less water. At any state of technology, we and our descendants will balance the costs of conservation measures against the cost of getting more water.


Fresh water can be obtained in unlimited quantity from the ocean by separating the salts from seawater. The only problem is the required energy and the capital cost of the equipment. During the recent water shortage in California, the city of Santa Barbara built a desalination plant that would have produced fresh water at a cost of $2,000 per acre-foot. Fortunately, the drought ended just as the plant was completed, and Santa Barbara never operated the plant. (I was told that the particular proposal chosen was not the least expensive but involved, as municipal projects sometimes do, some under-the-table payments.)

$2,000 per acre-foot is bearable for municipal water, but not for agricultural water under present conditions, because agriculture in one location must compete with agriculture in regions with adequate water supply.

However, imagine that California had to get its entire water supply of 35 million acre-feet per year by desalinating sea water at the Santa Barbara price. This would come to $70 billion per year, which is on the order of ten percent of the state's GDP. We'd survive, but it would be a blow to our standard of living, and the arguments about whose fault it was and how the cost should be allocated would be exciting. I'm assuming that the need to overcome the water shortage would overcome the objections to using nuclear energy to power desalination, because there probably isn't enough available natural gas.

2002 February: An email from the California Department of Water Resources lists the following amounts of water used for three uses, the latest figures being 1995. The amounts are in thousands of acre-feet.
08,770 urban
33,780 agriculture
36,940 environmental
79,490 total

The environmental use refers to keeping flows in rivers for environmental reasons. These flows existed previously but weren't counted as uses.

The Metropolitan Water District of Southern California announced in a 1996 press release its participation in funding a technology that would produce desalinated seawater for $800 per acre-foot. I think that if California had to rely on water at that price, the economy would not change much, although we probably wouldn't use it to grow much alfalfa.

The 2001 June 21 New York Times Has an article about a project to build a desalination plant in Ashkelon, Israel producing 36 million gallons per day at a cost $2.00 per thousand gallons, which comes to $650 per acre-foot. If California had to get all its water at that price, it would come to 3 percent of the state's GDP. That would make very little difference to the California's standard of living.

Ed Fredkin developed the following idea. A reverse osmosis separator is located 1800 feet underground. The seawater is pressurized to about 200 lb/in^2 on the surface but gets additional pressure from the 1800 feet of head. The brine is still at high pressure and requires very little pumping to get it to the surface where it is dumped back into the ocean. The fresh water is at low pressure, and energy is required to pump it to the surface. However, there is a large water storage cavern underground, so the pumping can be done at the hours most convenient for the electric company, the capital cost of pumps being cheap. Fredkin will supply me with estimated costs of his old proposal if he can find the disk, but he recalls they are quite a bit below the $800 per acre-foot that the Metropolitan Water District of Southern California is hoping for.

There are probably even better schemes than Fredkin's waiting to be invented.

The Middle East

Water supply is tightest in the Middle East. Of all the countries, only Saudi Arabia and the Gulf Emirates can afford the energy required for large scale desalination at present energy costs and with present technology. The water is supplied to agriculture at a subsidized price, because these countries want to develop agriculture. In the long run, all these countries will be rich enough to afford desalination if that turns out to be the most effective way to get the water. Israel is the country that has developed the most technology for irrigating crops as economically as possible.

Using Water Economically

There is a lot of sense and a lot of nonsense about economizing on water.

Nonsense first:

Every now and then there is a water shortage in some locality. California, where I live, had seven years of drought in the late 80s and early 90s. This generated some useful water saving measures and a lot of gestures. The extreme of the gestures was a request to restaurants to serve water only if requested by the patron. Here's the arithmetic on that one. Suppose a person drank the 8 glasses of water per day recommended by some health advocates (which almost no-one does). That's a half gallon per day or 183 gallons per year. Each Californian's "share" of the state's annual 35 million acre-feet is about one acre-foot. An acre-foot is 326,000 gallons, so a Californian is advised to drink one part in 1781 of his share. If all we had to worry about was drinking water, Perrier could be flown in from France. The advice about not flushing toilets so often was almost as silly. Restrictions on watering lawns begin to make sense in municipalities that are short.

Now the sense:

While the main burden of this page is that we can have all the water we want, there are enormous opportunities for economizing water, and often it is cheaper to economize than to get new supplies.

  1. Apparently, the single biggest thing many municipalities can do to economize on water is to fix leaks in the water distribution system.

  2. Drip irrigation, where the water is delivered directly to each plant saves a lot. (I'll put in the numbers when I get them.)

  3. Tomatoes grown hydroponically use 1/29 th the water of tomatoes grown in fields.

  4. Some crops, e.g. alfalfa for animal feed, may not be economical at present prices for farmers who have to pay full costs of irrigation water. Let alfalfa be grown for now where there is enough rain. Perhaps later the need and price for alfalfa will grow to the point where it can support the full cost of irrigation water.


The most authoritative information on water supply comes from the National Research Council. Its Water Science and Technology Board has published many relevant reports, most of which are on-line at the above URL.

Here's a California report on desalination.

There is a Groundwater Mailing List that you can subscribe to. I haven't - for fear of being overwhelmed. Unfortunately, they don't put the messages on their Web site.

Here's a somewhat scare-mongering UN report. It scarcely mentions supply technology, concentrating on using less water.

Sandra Postel of Worldwatch is quoted in Garden State Environews for 1999 October 10 as saying

Hydrologists estimate that when the amount of fresh water per person in a country drops below 1,700 cubic meters per year the country is facing water stress. In her book, Ms. Sandra Postel reports that the number of people living in countries experiencing water stress will increase from 467 million in 1995 to over three billion by 2025 as population continues to grow. In effect, these people will not have enough water to produce food and satisfy residential and other needs.

I find this puzzling. California has a population of 32 million and uses 35 million acre-feet of water per year. An acre-foot is 1233 cubic meters, so California is well into Postel's alleged water stress regime. Yet California produces the most agricultural products of any state in the US (in dollar value, I suppose) including considerable alfalfa and rice. We water our lawns, etc. Perhaps my figures are wrong, but I suspect hers.

Scientific American for February 2001 has a number of articles on water supply, including one by the above-mentioned Sandra Postel. There is a bit of scare-mongering, as is common among people hoping to attract resources to their own field. The main emphasis is on using less water rather than on getting more. This is in accordance with the green ideology that also wants us to use less energy and which bears a good part of the responsibility for the California electricity crisis of early 2001. The ideology is also likely to result in failing to build new water supply facilities in a timely way just as it resulted in failing to build new power plants.

HOH Canarias S.A. sells reverse osmosis seawater desalination plants claimed to use only 2.8 kwh of electricity per cubic meter of fresh water obtained. An acre-foot, the unit by which water is sold in the US is 1233 cubic meters, so we are looking at 3452 kwh per acre-foot. The cost of electricity is quite variable these days, but suppose we take $0.05 per kwh, which gives $172.60 per acre-foot for energy cost. Agriculture can afford that. While energy is the main cost of desalination, there are other costs also.

There is a relevant article "What Drives Societal Collapse?" by Harvey Weiss and Raymond S. Bradley in Science for 2001 January 26. According to the authors, who are archeologists, many civilizations have collapsed, and the most common cause is a prolonged drought. These occur every thousand years, more or less, in some important area of the world. Such droughts, lasting for hundreds of years, have occurred in the Americas as well as in the old world.

Fortunately, our civilization has reached a technological level at which we can deal with such prolonged droughts, e.g. by using nuclear energy to desalinate millions of acre-feet of seawater and pumping the water to where it is needed. Perhaps our descendants will be able to control the climate well enough to anticipate and prevent the droughts. We can't do that today.

Here are a lot of links to sites concerned with water.

Water Online bills itself as The Marketplace for Professionals in the Water and Wastewater Industry.

Findh20 is a commercial outfit with a database of world water resources and offering water finding services.

This page is part of a collection of pages on the sustainability of material progress. I am not professionally involved in water supply problems.

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I welcome comments. Send them to

John McCarthy

The number of hits on this page since 1996 January 16.