10. Water



Where in the world is all the fresh water

Through the hydrologic cycle, water constantly moves among the oceans, the atmosphere, the Earth’s surface, and underground. Of all this water, only 3 per cent is freshwater. Most of this freshwater (about 69 per cent of it) is currently stored as ice in glaciers and ice sheets; the rest is stored and flowing as lakes, ponds, and rivers (about 0.3 per cent) or as groundwater beneath the Earth’s surface (about 30 per cent). Less than 1 per cent of the world’s freshwater is located in the atmosphere (in the form of precipitation).

To effectively use these freshwater resources, people must find ways to control the water flowing on the Earth’s surface or access the groundwater below.

Diverting surface flow

To use the freshwater that flows along Earth’s surface as rivers and streams, people change where it flows, or divert it. Diversion projects are basically just manmade structures that take water from one area and bring it to areas that need it.

Two of the most common diversion projects are:

Aqueducts: Aqueducts are canals or pipelines that carry water from its natural source to an area that needs it. Both New York City and Los Angeles use aqueducts to divert freshwater from distant sources (the Catskill Mountains for New York and the Colorado River for Los Angeles). This type of water diversion goes all the way back to ancient Greece and the Roman Empire, though today’s versions are much more efficient. Although diverting freshwater through aqueducts solves the problem of supplying water to large urban areas, doing so also creates problems. For one, the diverted water is no longer available in the ecosystem it originally flowed through for the organisms that depend on that water source for survival. Using aqueducts is also likely to negatively affect people outside the urban center who depend on the natural flow of the water for their freshwater.

Dams: A dam is a structure that blocks the flow of a river, creating a large reservoir, or lake behind it where the water is stored for human use. Humans use dams for many purposes, including the production of electricity through hydropower. But as with any manmade change to a natural system, creating dams has some negative consequences. For example, because of the way they’re constructed, dams flood large areas of land behind them, upriver, where the reservoir is located. In some instances, this flooding destroys villages and important ecosystems. Dams also obstruct the natural flow of water and sediment downstream, and this obstruction, in turn, affects fish migration and changes the natural evolution of river habitats.

Tapping what flows below: Groundwater

Most of the freshwater that people access flows underground. The freshwater that flows through rocks and open spaces below the Earth’s surface is called groundwater. Although the ground you walk on is solid, spaces between the particles of sediment, or even within certain types of rock, allow water to move from the surface into underground storage spaces called aquifers. Two types of aquifers are:

Unconfined aquifers: Water in an unconfined aquifer is stored in permeable rocks and sediment through which it can flow freely. Hence, water in this type of aquifer can flow to plant roots or bubble up to the surface as a spring. The water table is the boundary between the water-filled rock and sediment of an aquifer and the dry rock and sediment above it. Water that seeps into the ground through the water table when it rains refills or recharges, the groundwater in unconfined aquifers.

Confined aquifers: Confined aquifers are surrounded by impermeable layers of rock that don’t allow water to move through them. Thus, confined aquifers create underground storage containers for the water they contain. Because impermeable rock layers surround confined aquifers, they have a specific area of recharge, where freshwater from rainfall can enter and refill the aquifer. To withdraw groundwater stored in both types of aquifers, people dig wells.

Unfortunately, the rate of recharge for most groundwater aquifers is much slower than the rate of withdrawal through wells to meet human water needs. As a result, many existing wells are now dry wells, where no more water can be drawn, and cones of depression form in the water table. A cone of depression is an area where the water table dips because water has been withdrawn from that area of the aquifer faster than it could be recharged. Withdrawing groundwater from aquifers faster than it can be recharged can result in saltwater intrusions in coastal regions, where freshwater underground contacts the salt water of the ocean nearby. When a cone of depression occurs, the space created by the withdrawal of fresh water may fill up with salt water rather than fresh groundwater, hence the name saltwater intrusion. After saltwater has intruded into an aquifer, the aquifer is no longer a source of fresh water for the people and ecosystems that depend on it.

Conserving Fresh Water

One way to meet the freshwater needs of people and ecosystems is to use techniques of water conservation. Water conservation is the process of using less water, to begin with, and recycling or reusing as much water as possible. The goal of water conservation is to maintain a fresh water supply that can meet the needs of as many people as possible for as long as possible. Technological innovation has helped achieve much of the water conservation happening today. For example, water-efficient showerheads and toilets reduce the amount of household water use in many homes. A dual-flush toilet offers the user an option between a normal flush (approximately 2 gallons of water) for solid waste and a lighter flush (about 1 gallon) for liquid waste. Manufacturers are also producing more water-efficient washing machines and dishwashers.

Do-it-yourself water conservation

Conserving water is one of the easiest ways to reduce your impact on local water resources and the other organisms that depend on them. Here are some ways you can start conserving freshwater today:

Turn off the faucet while brushing your teeth or shaving.

Wash only full loads of laundry.

Position sprinklers to water the lawn and garden, not the sidewalk or driveway.

Plant native shrubs and groundcovers rather than grass in your landscaping.

Allow your lawn to go dormant for a few months in the summer.

Compost food waste instead of using the garbage disposal.

Repair leaky faucets indoors and outdoors.

Install aerators on all your faucets.

Upgrade to more-water-efficient appliances, including toilets, showerheads, washing machines, refrigerators, and dishwashers.

Collect rainwater from your roof in rain barrels and reuse it to water your garden.

Rinse vegetables in a dish of water and then dump that water in your houseplant or garden.

Another approach to water conservation is to recycle freshwater within your home through a greywater reuse system. The term greywater refers to the wastewater from your sinks, showers, and washing machines (everything except your toilet water, which is considered sewage). Although you can’t use greywater for drinking, you can use it to water your lawn or flush your toilet. A greywater reuse system filters your home’s greywater so that it can be reused for other domestic freshwater needs.

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