Water: Quality And Quantity

The Center For Remote Sensing

It travels in a large, continuous cycle that is called the Hydrological Cycle. There are five processes at work in the hydrological cycle: evaporation (from the surface) and evapo-transpiration (from plants) that introduce water into the atmosphere; condensation of the water vapor (cloud formation); precipitation (rain); infiltration (water seeps into the ground); and runoff (water present in streams, rivers, lakes and oceans).

Water Quality and Quantity

The challenges of ensuring good water quality and quantity are becoming increasingly prominent as populations increase.

The water that we drink today may have passed through the hydrological cycle many times and could have existed when dinosaurs roamed the Earth hundreds of millions of years ago.

97% of the world’s water is in the saline ocean. Of the 3% that is fresh, 68.7% is in the form of snow and ice, mainly in the polar regions; 0.86% is in the form of permafrost; 30.1% is in groundwater aquifers (many of which are brackish), and just 0.34% is in rivers, lakes or wetlands.

People can only directly access groundwater and river water. Together they make up just 1% of the planet’s water and most of this is not evenly distributed. Historically to make water more freely available to humans, it was popular to build dams on river systems to store it, or to transfer it from one area to another via pipelines.

These days, as the world’s population is increasing, more of the surface and underground water supplies have been used and contaminated, and less fresh water is available. The quality of our water, therefore, is becoming as much of a concern as the quantity.

This makes it necessary to ensure that adequate, high-quality and sustainable water supplies can still be made available for this and future generations. Presently, there are three ways to do this. The first is water recycling, the second desalination and the third conservation.

Water Recycling

Water recycling can also be called water reclamation or water reuse. Normally the term recycling is used when applied to newspapers or aluminum cans etc., or when the hydrological cycle is discussed. Here, water recycling refers to reusing well-treated wastewater for beneficial purposes such as landscape irrigation (e.g., golf courses or public parks), toilet flushing, or with more rigorous treatment, for agricultural purposes or for replenishing a groundwater aquifer (referred to as groundwater recharge). It can also be used to create or enhance wetlands and riparian habitats.

There are many positive benefits to recycling water. Not only does it curb the amount of fresh water we consume, but it also decreases wastewater discharges and the associated effects of pollution.


Desalination is the process of removing salt from water. Filtering salt from water is not a new idea - for hundreds of millions of years, marine plants and animals have evolved unique methods of desalination. For example, salt glands discharge excess salt through the nostrils of iguanas, the eyes of sea turtles, and the tongues of crocodiles.

Humans began to desalt water mechanically in the first half of the twentieth century. By the 1960s, five desalination plants had been built worldwide. These days, 12,500 desalination plants exist in 120 countries, most of them being in the Middle East (especially the Arabian Gulf, where 52% of the plants exist) or the Caribbean.

In the Middle East, most desalted water is produced by distillation, which imitates the hydrological cycle. This means the salt water is heated so water vapor will form. This vapor eventually condenses when it is collected and cooled.

The end product is fresh water. In North America, a different desalination technique is used that is called reverse osmosis. In this procedure, water is forced through a series of membranes that are made up of tiny pores, as small as the size of one millionth of the thickness of a human hair, which trap the salts.

Desalination is still a very expensive process but very much welcomed in areas with limited supplies of freshwater, for example in Kuwait, Saudi Arabia, Morocco, the U.A.E. and the states of Florida and California in North America.

Today, the treatment cost of a gallon of purified seawater is 5 to 6 times greater than freshwater, so money is being invested in research and development to make it cheaper. Even so, the American Water Works Association forecasts that the world market for desalinated water will grow by more than $70 billion in the next 20 years.

Desalination plants could be used all over the world. They simply require a salty water source; an energy source to operate the plant; and a circulation pattern that effectively removes the discharged brine for coastal locations, or a way of managing it for brackish groundwater sources.

Thus, desalination plants must be located carefully to reduce environmental impacts. If used wisely, they may become a preferable option to over pumping sweet groundwater or diverting and damming rivers.


Whereas desalination is designed to produce “new” water sources, conservation strives to save and reduce water use. A good example of this practice is seen in the city of Denver in Colorado in the inland western parts of North America. It is a water producing state because it has numerous mountain ranges with many rivers. The most famous of these is the Colorado River.

This river system is huge, straddling several states, and extending all the way to Mexico. It provides water to millions of people in the Colorado Basin, as well as to wildlife and the surrounding ecological systems. Some of the water is also diverted, for example, to California.

In 1982, there was a growth boom in Denver, and it was proposed that a new dam be built to divert water from one of the tributaries of the Colorado River. An outpouring of protests ensued from fisherman, environmentalists, biologists and citizens, because the spawning grounds of fish would have been damaged; the migration of cranes would have been affected (since the blockage of flow would alter their habitats); and a canyon would have been flooded, etc. So the project was vetoed by the American Environmental Protection Agency (EPA) and the dam was not allowed to be built.

Most of the Colorado River water was already being used in some way. Therefore, conservational practices had to be invoked in order to reduce water consumption while still supporting the growing population. This was done in several different ways, as detailed below, depending on how the water was used.

Residents were encouraged to:

  • Install and use high efficiency plumbing fixtures. They were educated in water-saving habits, such as, low-flow shower heads and 1.6 gallon toilets to replace the older 6 gallon versions. In eastern Los Angeles, 8 million gallons of water are saved daily through the use of 1.6 gallon toilets;
  • Plant water-efficient landscapes through a method called Xeriscape, whereby plants are selected that are native to a region, or plants are grown that require smaller amounts of water, e.g., buffalo grass;
  • Meter water and pay for what they use; and
  • Reduce usage at peak times so that additional pumps and treatment plants do not have to be built.

Farmers who irrigate were encouraged to:

  • Improve application practices. For example, by using drip irrigation techniques and soil moisture sensors so that water is applied only when the soil needs it; and
  • Increase the uniformity of water application, so using less water.

Finally, industries were encouraged to:

  • Install water saving appliances; and
  • Reuse water used in manufacturing to run on site cooling (air conditioning) and sanitation systems, etc.

Thus, conservation applies the principle that one gallon of water saved is better than one gallon of water supplied. In the case of Denver, this approach worked and the dam was not built.

It is clear that water is an essential resource for human well-being, but there is a fixed amount of it on Earth. This is a good realization in our daily lives, as it can help us to see and respect water in a whole new light!

Center for Remote Sensing, Boston University, Boston, MA 02115

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