A confined aquifer is an aquifer below the land surface that is saturated with water. Layers of impermeable material are both above and below the aquifer, causing it to be under pressure so that when the aquifer is penetrated by a well, the water will rise above the top of the aquifer.

Unconfined aquifers are those into which water seeps from the ground surface directly above the aquifer. Confined aquifers are those in which an impermeable dirt/rock layer exists that prevents water from seeping into the aquifer from the ground surface located directly above.

Aquifers come in two types. Some are formed in the space between porous materials such as sand, gravel, silt or clay and are known as alluvial aquifers (sediments deposited by flowing water) or unconfined aquifers.

Unconfined aquifers are where the rock is directly open at the surface of the ground and groundwater is directly recharged, for example by rainfall or snow melt. Confined aquifers are where thick deposits overly the aquifer and confine it from the Earth’s surface or other rocks.

Within 50 years, the entire aquifer is expected be 70% depleted. Some observers blame this situation on periodic drought. Others point to farmers, since irrigation accounts for 90% of Ogallala groundwater withdrawals.

The Ogallala Aquifer, also known as the High Plains Aquifer, underlies eight different states, stretching across America’s High Plains from South Dakota down to Northern Texas.

The Ogallala Aquifer is being both depleted and polluted. Irrigation withdraws much groundwater, yet little of it is replaced by recharge. Since large-scale irrigation began in the 1940s, water levels have declined more than 30 meters (100 feet) in parts of Kansas, New Mexico, Oklahoma, and Texas.

Most of the water in the aquifer comes from precipitation on the High Plains. With the increase of irrigated agriculture, water levels have dropped in places where the groundwater from the aquifer was pumped out faster than water from precipitation moved through the sediments and rocks to replace it.

The ocean holds about 97 percent of the Earth’s water; the remaining three percent is found in glaciers and ice, below the ground, in rivers and lakes. Of the world’s total water supply of about 332 million cubic miles of water, about 97 percent is found in the ocean.

Chocolate tops the list with 17,196 litres of water need to produce 1kg of the product. Beef, sheep and pork meat all require high volumes of water for production also. Tea, beer and wine use the least according to the list.

Rice needs water for evapotranspiration, seepage and percolation, as well as for management practices such as land preparation and drainage. Submerged rice cultivation practices help to promote water percolation and groundwater recharge, control flooding during heavy rains, and prevent weed growth in rice fields.