15-6 Tapping Groundwater, Converting Saltwater to Freshwater, Seeding Clouds and Towing Icebergs

What Are the Advantages and Disadvantages of Withdrawing Groundwater? Avoid Too Many Straws in the Glass

Aquifers provide drinking water for about one-fourth of the world’s people. In Canada and the United States, water pumped from aquifers supplies almost all of the drinking water in rural areas as well as most of the water used in agriculture.

Relying more on groundwater has advantages and disadvantages:

  • Advantage: Aquifers are widely available and are renewable sources of water as long as the water is not withdrawn faster than it is replaced and as long as the aquifers do not become contaminated.

  • Disadvantages:

    • Water tables are falling in many areas of the world as the rate of pumping out water (mostly to irrigate crops) exceeds the rate of natural recharge from precipitation.

    • Covering aquifer recharge areas with urban development also contributes to aquifer depletion.

    • Overpumping aquifers is increasing the gap between the rich and poor in some areas. As water tables drop, farmers must drill deeper wells, buy larger pumps, and use more electricity to run the pumps.

    • Withdrawing lots of water sometimes allows the sand and rock in aquifers to collapse, causing the land above the aquifer to subside or sink.

    • Groundwater overdrafts near coastal areas can contaminate groundwater supplies by causing intrusion of salt water into freshwater aquifers used to supply water for irrigation and domestic purposes.

Can Deep Aquifers Supply More Water? Solution or Pipe Dream

With global water shortages looming, scientists are evaluating deep aquifers—found at depths of 0.8 kilometre (0.5 mile) or more—as future water sources. Some of these are gigantic nonrenewable aquifers containing deposits of water as much as a million years old.

There are two major concerns about tapping these mostly one-time deposits. One is that we know little about the geological and ecological impacts of pumping from deep aquifers. The other is that no international water treaties govern the rights to and ownership of water that underlies several countries.

How Useful Is Desalination? A Costly Option

Desalination involves removing dissolved salts from ocean water or from brackish (slightly salty) water in aquifers or lakes. It is another way to increase supplies of fresh water.

  • One method for desalinating water is distillation— heating salt water until it evaporates, leaves behind salts in solid form, and condenses as fresh water.

  • Another method is reverse osmosis—pumping salt water at high pressure through a thin membrane with pores that allow water molecules, but not most dis- solved salts, to pass through.

There are two major problems with the wide- spread use of desalination:

  1. One is the high cost because it takes a lot of energy to desalinate water. Currently, desalinating water costs two to three times as much as the conventional purification of fresh water.

  2. The second problem is that desalination produces large quantities of briny wastewater that contains lots of salt and other minerals. Dumping concentrated brine into a nearby ocean increases the salinity of the ocean water, which threatens food resources and aquatic life in the vicinity.

Can Cloud Seeding and Towing Icebergs or Gigantic Water Bags Improve Water Supplies? Solutions or Pipe Dreams?

For decades, 10 states, mostly in the water-short western United States, and 24 other countries have experimented with seeding clouds with dry ice or tiny particles of chemicals such as silver iodide. The hypothesis is that the particles become nuclei around which raindrops form and thus produce more rain or snow over dry regions and more snow over mountains. However there are the following issues:

  • Cloud seeding does not work well in very dry areas where rain is needed most, because there are few clouds to seed.

  • Although some proponents in the multimillion-dollar cloud-seeding industry say the technology works, a 2003 report by the U.S. National Academy of Sciences says there is no compelling scientific evidence that it does.

  • It introduces large amounts of the cloud-seeding chemicals into soil and water systems, possibly harming people, wildlife, and agricultural productivity.

  • Seeding has led to legal disputes over the ownership of cloud water. For example, during a 1977 drought the attorney general of Idaho accused officials in neighbouring Washington State of “cloud rustling” and threatened to file suit in federal court