Probably the most known concepts in economics, supply and demand make up the ending of market economies. Demand refers to how much of a product or service is desired by buyers. The quantity demanded is the amount of a certain product people are willing to buy at a certain price, and the relationship between price and quantity demanded is known as the demand relationship. Supply represents how much the market can offer. The quantity supplied refers to the amount of a certain good producers are willing to supply when receiving a certain price. The relation between price and how much of a good or service is supplied into the market is known as the supply relationship. Price then, is a reflection of supply and demand.
An example of supply and demand that consumers want and need is water. Water is one of the Earth's natural resources. Most of the world's water supply is saltwater stored in the oceans. The type of water we generally use in human activities is fresh water. Only 3% of the world's water supply is fresh water and two-thirds of that is frozen, forming the polar ice caps, glaciers, and icebergs. The remaining 1% of the total world water supply is freshwater available as either surface water or ground water; ground water accounts for two-thirds of this amount. Surface water is water that is visible above the ground surface, such as creeks, rivers, ponds and lakes. Ground water is water that either fills the spaces between soil particles or penetrates the cracks and spaces within rocks. Most people get their water from ground water sources. Millions more get their water from private wells, which also tap ground water sources. Ground water systems tend to serve smaller numbers of people, while surface water systems generally serve large populations. In the United States, 450 billion gallons of water are used per day from ground and surface waters for a variety of uses. Of those 450 billion gallons, only 100 billion gallons are actually consumed.
