When the sprinklers are running but the grass is still dry

Have you ever wondered why some parts of your lawn remain stubbornly dry even on days when the sprinklers have run? You might be surprised to learn that water pressure is often to blame.

According to Lindsay Brown, most cities serve homes with water at a pressure of about 60 psi (pounds per square inch). However, most sprinklers are designed to function best at a lower pressure – 45 psi for rotor style sprinklers and 30 psi for spray sprinklers. As a result, irrigation systems end up overwatering some parts of the lawn while under-watering others.stretch-of-lawn

Brown studied the impact of mismatched water pressure on water use in Woodbury as part of her internship project with the Minnesota Technical Assistance Program (MnTAP) this summer. Like most communities, municipal water use in Woodbury spikes during the summer when people are watering lawns and gardens. Residents use three times as much water during the summer as during the winter, and 42% of the city’s water goes to irrigation.

All of this water use has put a strain on the aquifer below ground that supplies drinking water for Woodbury and other communities, and the problem is expected to grow worse as Woodbury continues to grow. Several years ago, the Metropolitan Council issued a warning that Woodbury might need to find a new source of water in the future, a change that would cost millions of dollars. In response, the city set a goal of keeping citywide water use flat even as population is predicted to grow 34% by 2040.

2030 projected drawdown
In 2010, the Metropolitan Council predicted that there would be major draw-down of the Prairie du Chien / Jordan Aquifer in portions of Dakota and Washington Counties unless communities reduce water use.

During 2017 and 2018, Woodbury began a pilot program to distribute irrigation controllers to residents at a discounted rate. The “smart” controllers help to keep systems from turning on during or after it rains, and can also be used to divide yards into zones so that drier, sandy areas get more water than naturally soggy spots. City staff estimate that residents save an average of 30,000 gallons of water per year by switching to smart controllers.

For her project, Brown followed up with six randomly selected homeowners who had installed irrigation controllers, and conducted comprehensive audits of their irrigation systems. Based on her findings, she predicts that most people could save an additional 23,000-59,000 gallons per year by replacing their existing sprinkler heads with pressure-regulated sprinklers that work better with high water pressure.

If the thought of replacing every sprinkler in your lawn sounds like a daunting task, Brown recommends contacting an irrigation contractor to help navigate the process. She also suggests turning on your sprinklers to see what they do as a good first step. “Every home I audited during this project had at least one broken sprinkler,” she says. “I think that most people never look at their system while it’s running to realize that water is shooting onto the sidewalk or leaking from a broken head.” Fixing these problems can help you to keep your lawn green without wasting water. Brown also notes that you can save plenty of water simply by following recommended guidelines for lawn care in Minnesota, “Just because you have the option to water every other day doesn’t mean you should. Your lawn only needs one inch of water per week, including rainfall.”

Most people run their sprinklers in the early morning while they’re still sleeping. Try yours out over the weekend to see if there are broken heads or sprinklers shooting water into the road.

MnTAP is an outreach program of the University of Minnesota. In recent years, Washington County has partnered with MnTAP to offer free, in-depth water efficiency consultations for local businesses and specially trained summer interns to help implement water-saving projects. Previous MnTAP interns have worked with Bailey Nurseries in Cottage Grove and DiaSorin in Stillwater. Learn more about the program at www.mntap.umn.edu.

Look to University of Minnesota Extension for tips on how to get a greener, healthy lawn without using too much water.