The Quest for a Suitable Source of Alternative Irrigation Water

HRI-Funded, Multi-Year Project Targets Graywater Sources

Water is the most valuable resource we have. Everyone is familiar with the current crisis in California, where the severe drought continues. 2016 marks California’s fifth consecutive year of drought, which is not expected to end anytime soon. The problem, however, is bigger than just the State of California. With a warming climate, 80% of state water managers expect water shortages in some portion of their state over the next decade.


Agriculture is a big sink for water use. The USDA estimates that agriculture accounts for approximately 80% of the consumptive water use, or water permanently removed from available supplies and no longer available, in the US. This figure rises to 90% in western states. In 2015, California enacted its first ever restrictions on water usage for agricultural purposes in certain watersheds, and large farms will be required to report usage.


As water supplies become more limited and expensive, there is concern in the green industry that agricultural water needs for edible crops will eclipse those of ornamental crops. While some agricultural areas were targeted for water restrictions in California, the focus, up to now, has largely been on urban areas. State officials specifically targeted reductions in the amount of water used for lawns and other landscape plants, citing that these uses account for the biggest share of residential water use. Golf courses were also singled out in California and mandated to use 25% less water (as compared with 2013 levels) or water only two times per week (as opposed to daily).


With the threat of reduced accessibility to high quality water drawing nigh and given the necessity of irrigation by all nursery and greenhouse operations at some point in production, the green industry must consider water-saving techniques. Innovative conservation strategies, improved irrigation systems, and alternatives are more important than ever.


Pete House, former president of the New England Nursery Association and current vice president of East Haven Landscape Products, commented that there is no single topic more important to nursery production than water. He added, “Most states regulate water in response to drought, and too many regulations are based on fear and not on fact. We need science and research on graywater to provide the facts. It’s better to be proactive.”


“Graywater is produced by almost everybody and, in most cases, is wasted. The safe and efficient use of graywater is of paramount concern. Dr. Cabrera’s research addresses these issues in the green industry.”


Dr. Raul Cabrera, Rutgers University, is studying the use of alternative, low quality water sources for landscape and nursery irrigation purposes. Specifically, he is looking at graywater, which is basically all household wastewater not generated from toilets (which is blackwater). Another potential wastewater source is municipal reclaimed water, or former sewage minus the solids.


US households generate an average 21 gallons of graywater per capita per day. About 36% of this, or 7.6 gallons per capita per day, is from laundry water, which typically ends up in the sewer system. In states such as California, Arizona, New Mexico and Texas, where drought is commonplace, graywater has gained acceptance for use in urban/residential landscapes. Potable water savings are estimated at around 5% when laundry-to-landscape graywater systems are deployed by 50% of the residential population.  However, the impact on landscape plants is poorly documented. Dr. Cabrera aims to solve this mystery through a multi-year grant by HRI looking at the long-term effects of graywater on landscape plants, where he is mimicking laundry water with concentrations of laundry detergent, fabric softener, and/or bleach. Dr. Cabrera has also received support for this project through the USDA-ARS Floriculture and Nursery Research Initiative.


Larry Cammarata, Principle Sustainability Consultant with Certified Consultants Ltd., designs alternative irrigation systems based in the Midwest. Cammarata commented, “I love the idea! Let’s continue to explore alternative water sources. In the Midwest, rain collection is far more common than using laundry water, but this is still considered a new technology to residents and landscape architects. The square footage to be irrigated, the plant type(s), stage of development, and water requirements, and the soil type are all important considerations. Choosing the right plant for the right place with the right soil is key. For example, bald cypress is a poor choice as a parking lot tree.”


Cammarata has seen first hand the potential downside of alternative irrigation sources in the form of nutrient load and pH, when an office park solely utilized municipal reclaimed water for the turf and landscape. “Over time, the soil chemistry and physical structure changed, and the plants suffered,” Cammarata reported. The nutrient load of graywater is one of the critical components that Dr. Cabrera is studying.


Wastewater in general (and especially laundry water) is known to have high concentrations of Na+, Cl-, and B. Too much Na+ can negatively impact plant health and growth; this is well documented. In a study published in 2005, researchers from Colorado State University reported needle burn of ponderosa pine after four years of irrigation with recycled wastewater, likely related to a Na+ concentration of 11 times that of pines treated with surface water. Preliminary data generated by Dr. Cabrera show that plant growth and quality lessen when bleach is a component of the graywater. An undesirably high pH is also a common trait of graywater.

Dr. Cabrera’s study is in early stages of development. So far, growth and quality data have been collected from twelve different ornamental plants irrigated with graywater for six months in Texas. A similar study will be initiated in New Jersey this year that will continue at least until 2018. In addition to growth and quality ratings, leaf tissue and soil samples will be collected, and a survey will be prepared to assess the current use and interest of alternative irrigation in the green industry.


While graywater has greater application in residential landscape settings, nursery and greenhouse operations will have greater use for reclaimed water from municipal sources. Graywater and reclaimed water are similar in their composition; the main difference being a greater presence of Cl- and surfactants in graywater. Soil structure and soil microbial populations will be evaluated in Dr. Cabrera’s project. Based on the study design, results will be relevant to both residential landscape and greenhouse/nursery settings.