Over the years, many progressive communities have found uses for reclaimed,
or recycled, water to both conserve fresh water supplies and enhance economic
growth and development. While some drought‑prone and arid regions have
used reclaimed water since the 1920s, more cities and regions worldwide are
now building water reclamation into their planning processes.
Florida’s water reuse program reclaimed approximately 738 million gallons
per day in 2015 alone—37 gallons per day per person. In a single year, Floridians
saved more than 144 billion gallons of fresh water while adding more than
86 billion gallons back to available groundwater supplies. Austin, Texas currently
has over 50 miles of reclaimed water pipes under its streets. The city’s code
requires new commercial developments or redevelopments within 250 feet of
a reclaimed water main to use reclaimed water for irrigation, cooling and other
non-potable applications. California has plans to increase its use of reclaimed
water by at least two million acre-feet per year by 2030. If the state can someday
reclaim and sell the estimated 4.5 million acre-feet of wastewater it produces
annually, it could generate up to $2.5 billion in much-needed revenue.
Clearly, the movement toward increased reclaimed water use is well under
way. Reclaimed water offers both benefits and challenges, and it has become
an integral part of Rain Bird’s efforts to help its customers meet their irrigation
needs. Rain Bird continues to develop and enhance irrigation system
components for use with reclaimed water, making it easier to irrigate with
water that was formerly discarded. Read on to learn more about reclaimed
water, benefits and challenges and how to implement it at your site.
Pros Vs Cons
Landscape irrigation has become the most common use for reclaimed water, and for good reason. According to the
EPA’s WaterSense Program, the average American family uses 320 gallons of water per day, about 30 percent of which
is devoted to outdoor uses. More than half of that outdoor water is used for watering lawns and gardens. Nationwide,
landscape irrigation is estimated to account for nearly one-third of all residential water use, totaling nearly 9 billion gallons
per day. It’s clear that replacing those billions of gallons of fresh water with reclaimed water could have a significant
impact on fresh water supplies here in the U.S. alone.
Reclaimed water’s nitrogen and phosphorus content can make it ideal for irrigation use, as those components are found
in most fertilizers. However, irrigating with reclaimed water also comes with its own unique set of challenges.
As water is reclaimed, its salinity level increases. Higher salt content can harm not only the soil and the fauna, but also the
irrigation equipment used to deliver this water. It may be necessary to “overwater” plants by about 10% depending on soil
and plant type to mitigate any possible negative effects. However, some plants, including turf grasses, deciduous trees
and most annual plants, tend to tolerate salt better than others. Selecting the right plants and managing irrigation wisely
will minimize the impact of higher salt levels.
The amount of treatment chemicals present in reclaimed water can spike significantly earlier in the day when water
systems are typically “shocked” to disinfect the reclaimed water line. Chemicals such as chlorine used to disinfect
reclaimed water can break down irrigation system components more quickly, as can the microbes and other solids
that typically remain after treatment. It’s also important for properties irrigating with reclaimed water to avoid overspray,
particularly in high-traffic areas.
Still, the potential benefits of reclaimed water use far outweigh the challenges. In addition to conserving potable
water, water reuse can save money, as reclaimed water rates are typically lower than drinking water rates. Perhaps
most importantly, reclaimed water use helps ensure that communities have enough water to meet their current and future needs.
Reclaimed water contains nutrients that can be used by plants. When irrigating with reclaimed water, these nutrients can likely replace some of the fertilizer that might otherwise be applied. This substitution can result in financial savings in fertilizer costs for reclaimed water users. For many individuals who decide to irrigate with reclaimed water the question may not be, “Can I reduce my fertilizer inputs?” but rather, “How much can I reduce my fertilizer inputs?”
Taking advantage of the nutrients in reclaimed water requires understanding and practicing several important aspects that greatly influence how effectively plants use nutrients. Irrigation systems must be operated, maintained, and calibrated properly to maximize the nutrient uptake efficiency of the plants. The seasonal variation in the supply of nutrients in reclaimed water should be taken into consideration to ensure that the amount of nutrients desired is supplied at the right time and can be effectively utilized by plants. Fertilization plans should be adjusted to account for the seasonal variation in the supply of nutrients from reclaimed water.
Several important aspects of reclaimed water irrigation must be understood and practiced to avoid unintended environmental impacts. Irrigation systems must be operated, maintained, and calibrated properly to avoid over-spray onto paved surfaces, over-irrigation, and leaching of the nutrients in reclaimed water or applied fertilizer. Applying fertilizer without accounting for the nutrients supplied by reclaimed water could result in applying more nutrients than plants can use or soil can retain. This can result in runoff and leaching of excess nutrients and pollution of lakes, river, streams, and groundwater.
It is important to note that the total amount of nutrients supplied when irrigating with reclaimed water is not necessarily the amount that plants can use. Effective utilization of the nutrients in reclaimed water will depend on the timing of supply and proper irrigation practices. This publication presents basic information for those using reclaimed water to irrigate lawns and landscapes. The information can serve as a guide to determine whether there is an opportunity to replace some of the fertilizer that might otherwise be applied and to offer guidance on avoiding runoff and leaching of excess nutrients.
What Nutrients Are in Reclaimed Water?
Nitrogen (N) and phosphorus (P) are the two primary nutrients found in reclaimed water. Other micronutrients are also found in small amounts. However, they are usually not included in routine analyses. Most of the N and P in reclaimed water are found in forms that plants can easily use (e.g., Duncan et al. 2009). For more information on the plant-availability of nutrients in reclaimed water and a summary of several research studies, see Martinez and Clark (2009; http://edis.ifas.ufl.edu/ae449). For more information on crop irrigation and types of micronutrients that can be found in reclaimed water, see Parsons (2009; http://edis.ifas.ufl.edu/hs1157).
How Much Nitrogen and Phosphorus Are in Reclaimed Water?
The amounts and forms of N and P in reclaimed water vary from utility to utility and can vary by time of the year. Therefore, quantities of N and P must be known to incorporate reclaimed water into a landscape fertilization plan. In addition, changes in water chemistry can occur between the point the reclaimed water leaves the treatment plant (where measurements are routinely taken) and the point of irrigation. The local utility that provides the reclaimed water can be a source for this information.
How to Calculate the Amount of Nitrogen and Phosphorus Supplied by Reclaimed Water
Calculating the amount of N and P applied when irrigating with reclaimed water is easy to do. All that must be known is the quantity of reclaimed water used for irrigation (in either inches or gallons) and the concentration of N and P in the reclaimed water, measured in either units of milligrams per liter (mg/L) or parts per million (ppm).
It is important to note that the amount of N and P applied when irrigating with reclaimed water is not necessarily the amount that can be used by the plant. Proper irrigation is extremely important to effectively utilize the N and P in reclaimed water. Over-irrigation will reduce the proportion of N and P that can be used by the plant, no matter what concentrations are present. In addition, the timing of application of N and P in reclaimed water is important for effective utilization. The importance of proper irrigation and the timing of the supply of N and P in reclaimed water are discussed in more detail in later sections of this publication.