The majority of fresh water flowing from the taps in the US, and the rest of the world, is derived from groundwater. Wide, flat stretches of porous, sandy material that lie in layers under the ground, are called aquifers if they also contain water. Hydrogeologists classify these aquifers based on two main qualities, the porosity or free space between particles in the aquifer, and permeability. Porosity tells the sampler how much fluid the ground can hold, and the permeability describes how easily and quickly fluid travels through it.
The best aquifers for tapping groundwater have both high porosity, high permeability, and are sandwiched safely between two impermeable layers of earth to keep the water separated from contaminants and contained. Materials like sand and gravel are typical of aquifers, while clays and silts will act like a water barrier, and are typical of aquitards.
Groundwater is a healthy, renewing supply of water, largely because rain water and farm run-off gets naturally filtered as it travels down through the earth on its way to the aquifer layer. If too much pumping is done, however, the aquifer sands may dry up and compress permanently, in a process known as subsidence. This sinking of the land after over-pumping is a big problem in places like Mexico city and southern Texas, where buildings have collapsed after the underlying aquifer was drained of water. Subsidence irreversibly dies up a previously fertile source of freshwater.
As so much of the agriculture industry depends on groundwater irrigation, especially when it comes to growing water-intensive crops like strawberries and tomatoes, it’s imperative that we protect these water supplies from over-pumping and contamination. Some ways to accomplish this would be to irrigate the fields when the sun is less intense, such as in the evenings and mornings, so that evaporation would be minimized. It is also interesting that certain products require much more water to produce than others. This is especially true if fruits, vegetables and even animals are produced in a drier climate than their native one, as they need more water than the new habitat can supply naturally to survive. Some examples would be the strawberries grown in Texas, as well as soybeans, corn, rice and alfalfa.
Another factor to consider is the lifespan of the organism being farmed, because the longer it lives, the more watering it will require before it can be sold and used to make a product. An interesting article in Discover Magazine has recently outlined just how much water goes into producing ordinary objects, and it came as a surprise that leather was at the top of the list. Water not only goes into the cow’s diet over the years it is alive, but it nourishes the grain that the cow eats, and is used to wash, cure, and produce leather products after the cow has stopped directly consuming freshwater.
Using groundwater for irrigation, however, is a very efficient way to make use of the water that is not clean enough for drinking water standards. That being said, the level of contaminants and potential toxins can not be excessive in irrigation water, and more pains should be taken by companies to reduce their water pollution. The three most common and dangerous sources of groundwater pollution are leaching from landfills, fertilizers, pesticides and wastes from farm runoff, and salt water from nearby ocean that is drawn by over-pumping.
Highly publicized cases of sickness caused by chemical leaks or bacterial contamination into groundwater, leading to birth defects, cancer and mental disabilities in affected communities, highlight how vulnerable the water sources and the people who depend on them are. Often, people have to become sick, or die, before any safety precautions are taken to protect aquifers from the damage our profit-oriented industries wreak.
As global warming creates a growing sense of unpredictability in weather systems and melts away the freshwater-rich glaciers, it’s comforting to be able to turn to a replenishable source of water that has a lifetime on the order of thousands of years. And like with any other natural resource, it needs to be tapped responsibly, and protected from careless contamination or outright destruction for future generations.
References:
Thomas M. Kostigen. Everything You Know About Water Conservation is Wrong.http://discovermagazine.com/2008/jun/28-everything-you-know-about-water-conservation-is-wrong/?searchterm=water
Ronald Neighbors. Subsidence in the Greater Houston Area- Past, Present and Future.http://www2.egr.uh.edu/~civeb1/CIGMAT/03_present/5.pdf
Frank J. Bove et al. Public Drinking Water Contamination and Birth Outcomes.http://aje.oxfordjournals.org/cgi/content/abstract/141/9/850
