More fresh water is used for agriculture and irrigation (75%) than any other industry despite the fact that many crops and livestock can tolerate a lesser quality of water than humans. (Dept Interior Oil & Gas Produced Water & Beneficial Use, September 2011). Produced water and other nonpotable water sources (like brackish aquifers) can be used to offset this demand. In fact in Texas, almost twice as much produced water is generated than is needed to water livestock and agriculture (excluding irrigation needs). However, being able to continually monitor these waters in the field is critical to their successful use.
While water under 10,000 mg/L of total dissolved solids (TDS) can generally be used for livestock, specific components of the dissolved solids must be monitored because certain livestock have varying tolerances of TDS and specific mineral components. For example for livestock watering, sulfate and alkalinity should not exceed 2,000 mg/L, pH should range between 5.5 and 8.5, and boron levels should not exceed 5 mg/L. Comparatively, TDS should be kept below 3,000 mg/L for poultry.
For irrigation, nonpotable water sources can also be reused in order to offset the tremendous reliance on fresh water. However, once again, the quality of the water must be monitored. For example, sodium adsorption rates (SAR) are critical. Not only must the SAR be monitored, but also pH and levels of boron, chloride, and nitrate levels (among others). Additionally, the volume of nonpotable water being used and its electrical conductivity must be monitored.
Agricultural runoff can be a serious problem for multiple reasons. It can be potentially disruptive to the local ecosystem. For most plant life as well as single celled organisms, growth is limited by access to phosphate, nitrate, and other compounds which are used as fertilizers. If a large amount of these compounds are introduced through runoff into an ecosystem in which they are naturally deficient, large blooms in algae and other organisms can have a devastating impact on other organisms. For example, during such a bloom, oxygen levels will drop dramatically causing the asphyxiation and death of local fish populations. If the chemicals in agricultural runoff make their way into a municipal water source, the local drinking water may be rendered non-potable.
In addition, loss of fertilizers to runoff is a source of inefficiency in the delivery of nutrients to crops. Agriculturalists typically will use an excess of fertilizers expecting a percentage of it to be lost to runoff before it can be absorbed by their crop.
Determining the presence of agricultural runoff in water sources is critical not only to assessing the extent of the chemical contamination, but also to determine the source of the contamination. If the contaminated water source is a moving body of water such as a river or stream then finding the source of contamination requires many samples to be taken at many locations.