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WATER FOOTPRINT
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A relatively new concept introduce in 2002, when the need was identified to establish a fresh water footprint similiar to the ecological footprint.
The water footprint is an indicator of water use that includes both direct and indirect water use of a consumer or producer. The water footprint of an individual, community or business is defined as the total volume of freshwater that is used to produce the goods and services consumed by the individual or community or produced by the business.
The Water Resources of Earth
Over 70% of our Earth's surface is covered by water. Never the less, water is seemingly abundant, the real issue is the amount of fresh water available.
- 97.5% of all water on Earth is salt water, leaving only 2.5% as fresh water
- Nearly 70% of that fresh water is frozen in the icecaps of Antarctica and Greenland; most of the remainder is present as soil moisture, or lies in deep underground aquifers as groundwater not accessible to human use.
- Less than 1% of the world's fresh water (~0.007% of all water on earth) is accessible for direct human uses. This is the water found in lakes, rivers, reservoirs and those underground sources that are shallow enough to be tapped at an affordable cost. Only this amount is regularly renewed by rain and snowfall, and is therefore available on a sustainable basis.
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Examples of Natural Water Purification
A green sand filter uses manganese green sand to filter iron, sulfur, hydrogen and manganese out of household and drinking water.
Sand filters (also called biofilters) are a biological way of purifying drinking water. Low turbidity is a requirement for sand filters to function effectively.
Sand and gravel nature's materials used to create a water filter. Yet water has been filtering through these substances underground for millions of years. The result is spring water, making up part of the cleanest water on Earth.
Spring water is pure precisely because it has filtered through porous layers of sediment. Pure spring water results from filtration through hundreds of feet of sediment, sand, and gravel, as with anything nature a extremely slow process. Studies estimate that water moves through most natural sediment filters at a rate of less than 0.1 gallon (0.4 liter) per minute for every square foot of area. As it moves through these layers, solids suspended in the water are trapped in the sediments. Disease-carrying microorganisms, such as bacteria, are also trapped, where nature has a way to eliminate them either they die naturally or become food for microorganisms that live in the sediment. Depending on where the water comes from, artesian springs or is pumped from aquifers, it is on average more than 99.9 percent free of contaminants.
Of course, pure spring water is not always easy to find. Surface water is much more readily available, but it often contains contaminants, including disease-causing organisms and toxic chemicals. In many places, groundwater is similarly contaminated. To make water from these sources safe to drink, most treatment facilities use processes and materials similar to those that remove contaminants in natural sediment filters. The objective of artificial filters, however, is to speed the filtration process and decrease the amount of space required for purification. Modern facilities use substances called coagulants to chemically trap particles and organisms, which are then easily skimmed off. Afterward, more fine-grained filtration and treatment with chemicals kill any remaining microorganisms.
In coastal desert regions, where freshwater of any kind is scarce, people have turned to the sea for their drinking water. Making seawater drinkable, however, requires more than simple filtration.
Distillation: In this process, seawater is evaporated, leaving the dissolved salt behind. The water vapor is condensed, at which time it is collected as pure, fresh water.
Reverse Osmosis: Uses high pressure to force water through a very fine-grained filter, called a semi-permeable membrane. This membrane allows water molecules to pass through, but not the larger sodium and chlorine ions.
Both reverse osmosis and distillation require a large amount of energy to turn seawater into drinking water and are consequently very expensive.
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