What can the grower do?

The individual grower can protect him/herself against future droughts, interruptions, higher water costs, and severe water shortages by tapping into the nearest available source of recycled water. Such sources can include:

• Major wastewater treatment facilities of large cities, many of which now are becoming recycled water production facilities
  
• Medium-sized wastewater treatment plants serving smaller rural communities
  
• Small or package treatment plants serving clusters of residences in isolated areas
  
• Gray water from an individual residence tapped for irrigation of a garden patch that might include food crops (exercising care to avoid exposure of edible portions of the crop to the untreated gray water.
  
• Tailwater from upstream furrow and flood irrigation practices with their inherent excesses and inefficiencies.

Reclaimed water from any of the first three sources can be conveyed either by gravity of pressure pipe to the farm and reused to free up drinking water. Gray water does not have a significant place in commercial agriculture, because of its relatively small volume and limited applicability. Tailwater reuse is a significant water source for farms where runoff at the end of the furrows is an inevitable consequence of surface irrigation. With laser leveling and highly controlled irrigation practices, tailwater is minimized on the more modern, well-operated farms. Nonetheless, tailwater is a potential water resource and can be captured for reuse.

Proactive use of recycled water by the farmer would involve input by the farmer in the microbial and chemical quality of the delivered recycled water. The level of treatment mandated by regulations is simply a floor—a minimum required quality that would protect the public health. Farmers need water quality that also protects their soils in the long-term use of recycled water. Wastewater treatment plants can change the chemicals they use for various treatment processes if they are given the necessary information and incentives to do so. Thus, growers should insist on a recycled water chemical quality with criteria that will not be injurious to their particular soil, crop, and climatic conditions. Because soils, cropping patterns and climatic conditions vary so much from one location to another, each farmer would need to determine the acceptable levels of these critical parameters for themselves.

Water Savings

Water savings achieved by using recycled water can range up to 100 percent of the demand, depending on the extent to which available recycled water must be supplemented with traditional sources of irrigation water. In some cases, river water or well water is supplemented with recycled water to produce a blend with a lower salinity than that of straight recycled water. Currently, farmers in California use roughly 250,000 acre-feet of recycled water each year for a wide variety of crops. There is significant opportunity to substantially expand the use of recycled water for agricultural irrigation.

Applications

The applicability of recycled water for agricultural irrigation is nearly universal. Limitations to its use are similar to limitations applicable to other sources of irrigation water—e.g., salinity, sodicity, presence of specific ions in higher concentrations than allowed in standard agronomic practice. In addition, the level of treatment that recycled water has received determines whether restrictions are imposed on allowed crops or not. Disinfected tertiary recycled water can be used for unrestricted irrigation of all crops, without any limitation on irrigation method employed. For a complete listing of allowed uses of recycled water at different treatment levels, click here.

Additional Benefits

Energy Savings with Recycled Water

The greatest hurdle to use of recycled water for irrigation is distance from the source of recycled water. Usually, farms are in rural areas located at long distances from urban centers and their wastewater treatment facilities. And, even if all urban reclaimed water could somehow be transferred to agriculture, the total agricultural demand for water is many times greater than the available supply of municipal recycled water. Thus, farm areas with close access to sources of recycled water are at a unique advantage over others especially in times of drought and in a future that is anticipated to be far more water-scarce in general.

Benefits for wastewater treatment plants

Most managers of wastewater treatment systems and their directors are now aware of the important water resource that their treated effluent potentially represents. They are also aware of the environmental impacts of their discharge to the environment. Thus, they are becoming increasingly motivated to find customers for their recycled water. Many public agencies invest huge amounts of resources in laying our infrastructure for distribution of the recycled water to the end users. In California, agriculture represents 40 percent of these end users of recycled water at the present time. The revenue from the sale of recycled water represents another incentive for communities with a significant volume of potentially recyclable water available for reuse. This is usually not a major motivator as the costs of treatment and distribution generally far outweigh the revenue. Therefore, federal and state governments have provided large subsidies to local agencies in recent years, in response to regional water shortages and droughts, to encourage water reuse.

Another major incentive for wastewater treatment plants to recycle their effluent is the upcoming tougher discharge requirements involving removal of minute concentrations of heavy metals and organic compounds through imposition of total maximum daily load (TMDL) regulations. The upper layer of farm soil and its rich microbial population can handle organic compounds that would otherwise be unhealthful if discharged to a surface water body, such as a river, lake or ocean. The soil does this by precipitating, absorbing, adsorbing, digesting, hydrolyzing, or decomposing organic compounds. Therefore, recycling water for agricultural and landscape irrigation is a far superior course of action for society than a high level of treatment for removal of another three or six logs of microconstituent concentration from the water. Even then, someone may ask if the remaining parts per trillion can harm fish or other amphibians in receiving waters.

Environmental benefits

Significant environmental benefits can be garnered by redirecting wastewater to fields that may otherwise degrade sensitive water bodies. Furthermore, recycling agricultural water can offset withdrawals from surface water, bolstering water flows for fish, other wildlife and plants.

Frequently Asked Questions about Recycled Water

Reuse of Agricultural Wastewater

Agricultural wastewater is primarily the excess water that runs off the field at the low end of furrows, border strips, basins, and flooded areas during surface irrigation. This wastewater is also referred to as irrigation tailwater. A certain amount of tailwater runoff is necessary to ensure adequate penetration of water along the length of the furrow or border strip being irrigated and to achieve a modicum of irrigation efficiency.

Another source of agricultural wastewater is effluent from plants processing crops harvested from the field and those preparing processed food, operated by and for farmers, usually in centralized facilities. These facilities generate considerable amounts of agricultural/industrial wastewater, typically containing high concentrations of organic matter. Often, effluent from these plants is sent to a nearby municipal wastewater treatment plant. Because of the absence of sanitary wastes in the agricultural processing plants, it would be best if their effluent were handled separately and made suitable for reuse.

Both of these sources of wastewater can be reclaimed and beneficially used—usually on the farms close to the location where the wastewater is generated. Runoff from the low end of furrows can be utilized for irrigation of fields at lower elevations without treatment and without pumping. In many cases, the runoff can be captured and stored in ponds for later reuse with a pump. This water should not be allowed to infiltrate into the groundwater aquifer, because of its chemical content. The ponds should be lined with impermeable clay or a membrane liner and the water should be reused as soon as possible.

In very large agricultural regions—such as the Central Valley of California—the cumulative flow of tailwater from many farms has historically posed significant environmental problems as it was discharged to surface waters—wetlands, streams, rivers, the San Francisco Bay Delta, and the Sacramento River, culminating in San Francisco Bay and the Pacific Ocean. These discharges are now prohibited. The discharge contains salts, nutrients, pesticides, herbicides, and other agricultural chemicals from the fields where they are used for crop protection and yield maximization. The collection of tailwater from these farms and its treatment and reuse is a win-win solution for the farmers and for the environment. The costs involved are well worthwhile, when compared to the benefits to the farmers and to society as a whole. However, short-term profit and lack of vision often prevent this solution from being implemented, unless mandated by law and supported with public monies.Agricultural wastewater from food processing plants is generally laden with organic matter (high biological oxygen demand—BOD), making treatment expensive and energy-intensive. Us of these wastewaters for soil conditioning and irrigation—at agronomic rates—can avoid the need for treatment while helping to improve soil organic content, soil tilth, soil cation exchange capacity, soil moisture holding capacity, and soil nutrient content and productivity. However, application of these wastewaters to the fields must be done with great care to avoid over-application, runoff, and groundwater contamination.

Photo by Los Muertos Crew

Water Savings

Where the most efficient irrigation methods (drip, tape, subsurface application, well-designed center-pivot, etc.) are already in use, there is no tailwater to reuse. Already, great savings have been realized over whatever practices were replaced. Where surface methods are in use, the savings in irrigation water volume can range from a few to over 50% depending on field slope, uniformity of topography, design of the fields, and manual and mechanical control mechanisms used on the farm.

Applications

In some cases, tailwater contains too much salt and nutrients to be used safely for irrigation of fields at lower elevation. Blending with lower-salinity source water can solve, or reduce this problem. In rare cases, desalination of tailwater may be an economic solution. The nutrient content of tailwater can be an asset if it is taken into account in application of commercial fertilizers where tailwater is used. Otherwise, it can lead to over-fertilization and groundwater contamination—especially with excess nitrogen.

Today’s farmers are sophisticated, much better educated than their grandparents, and tend to run their farms as businesses with a great deal of planning and agricultural engineering. For them, to put tailwater and food processing wastewater to beneficial use can be a profitable farm venture, if the long-term benefits of these practices are taken into account. They can look for opportunities to minimize or eliminate wastage of water and account for the resultant profits.

Additional Benefits

Collecting and reusing tailwater benefits the environment by avoiding discharge of salts, nutrients, and all kinds of agricultural chemicals into surface waters. The dissolved nutrients in tailwater can reduce the need for fertilization in the downstream fields where the water is reused. Tailwater reuse improves overall irrigation efficiency for surface irrigated farms. Another benefit is prevention of ponding at the low end of irrigated fields and the consequent loss of a portion of the crop.