redistributed for reuse. These are examples ofnon-consumptive water use.By recycling
water, we ultimately reduce our overall water consumption.
Unlike the previous examples, water sprinklers are calledconsumptive,because much of
the water is lost to the air as evaporation. None of the lost water can be captured and
reused.
Agricultural Water Uses
Have you ever watched huge sprinklers watering large fields of crops (Figure21.2)? If
you have, try to imagine how much water it takes to water a field compared to taking a
shower or bath. You may be surprised to learn that agriculture uses more than two thirds
(69%) of the water humans use, globally. http://authors.ck12.org/wiki/index.php/
File:Ear-2101-02.jpg
Figure 21.2: Agricultural Water Use: Overhead sprinklers need to use large quantities of
water on crops because much of the water is lost to evaporation and runoff. ( 25 )
Two of the most popular irrigation methods are overhead sprinklers and trench irrigation.
Trench irrigation systems are just that: trench canals that carry water from a water source
to the fields. Farmers often chose these methods because they relatively inexpensive. Unfor-
tunately, they are also wasteful of water. Roughly fifteen to thirty-six percent of the water
never reaches the crops, because it evaporates into the air or is lost as runoff. When rain or
irrigation water is not absorbed by the soil, often it washes valuable soil away.
Giving up irrigation is not a choice for most farmers. A farmer living in a dry region, such
as a desert, needs irrigation, just to grow crops. A farmer living in a wetter place would use