Keeping water on budget

April 14, 2015 -  By
iStock_Calculator. Photo: ©istock.com/denisenko

Photo: ©istock.com/denisenko

With water budgets, contractors can demonstrate and document good water stewardship.

When it comes to sustainability, few people are under more pressure than irrigation contractors. With droughts drying up entire regions throughout the U.S., municipalities are mandating that property owners significantly reduce their water usage—or even stop irrigating their landscapes altogether. Coming up with those savings often falls on contractors’ shoulders.

All this gives Brent Mecham “heartburn.” The industry development director for the Irrigation Association (IA) knows there are ways for contractors to be part of the solution, rather than the problem. Water budgeting is one of those ways that allows contractors to demonstrate and, more importantly, document their water stewardship while still doing their jobs.

“It’s a best-management practice,” Mecham said during an IA webinar about water budgeting. “It’s the right thing to be doing, and if we do it correctly we’ll be able to document and prove that we’re good stewards of water.”

A water budget provides a framework for determining the minimum amount of applied water required to produce the social, economic and environmental benefits of an irrigated landscape, according to the IA. Determining the correct inputs is a critical step in creating an effective water budget. Inputs to the water budget must be tailored to local conditions and based on sound science.

Contractors need to understand not only the plants, soil and workings of the property’s irrigation system, but also the purpose and function of the landscape, Mecham said. Then, they need to match the landscape’s demand to the available water supply, which will vary depending on location. Some locations have flexible water budgets, which change with the weather, allowing more water usage during hotter months and less water during colder or rainy months. Other locations have fixed water budgets, which are based on historical demand and do not respond to changing weather.

“If there’s a limited amount of water, then the landscape designer or architect needs to figure out what plants they’ll use, what kind of turfgrass and if it will be useful and purposeful, and then balance all of that,” Mecham said. “What we’re able to do dictates the look and style of the landscape.”

How to calculate

To calculate a water budget, contractors need to know several figures. The first is the Reference Evapotranspiration Data (ET°). Next, they need to know the Adjustment Factor (AF), which is the percentage of the Reference ET they’re going to allow for the landscape. Most of the time, this factor is 0.6 in areas that are water challenged and 0.8 in areas with high rainfall and more water available. The next factor is the Landscape Area (LA), the square footage of landscape to be maintained with irrigation. Lastly, they need the conversion factor (0.623) to convert all the units into gallons. Multiplying all these figures together determines the Landscape Water Allowance (LWA). This can be calculated monthly, annually or before every irrigation event.

In areas with poor water quality, an optional figure to include is the Leaching Factor (LF), which accounts for the extra water needed to push salts or other elements that could be detrimental to plants out of the root zone. This can equate to 20 percent to 25 percent more water than the ideal, Mecham said.

The next part of a water budget is the Landscape Water Requirement (LWR). To calculate it, multiply the Reference ET in inches by the Plant Factor (PF) and subtract the Effective Rainfall (Re) in inches. Multiple that figure by the Landscape Area (LA) and the 0.623 conversion factor, then divide by the Irrigation Efficiency (IE). The IE is the amount of additional water needed to compensate for an irrigation system’s lack of efficiency. For example, if a system is 90 percent efficient, which can be achieved with drip irrigation, it takes 10 percent or 11 percent more water than the ideal to maintain the landscape. If a system is 70 percent efficient, which Mecham said “sounds pretty good,” it will use 42 percent more water.

“In the end, what we’re striving to do is see if the water requirement is less than the water allowance, and if it is, we’re doing a great job,” Mecham said. “However, if the water requirement exceeds the water allowance, then management decisions need to be made.”

Mecham says these decisions can’t be made unless contractors measure how much water they use. While many irrigation systems, particularly on residential properties, don’t have dedicated water meters, Mecham said you can purchase one for about $100. They can be a good investment for contractors who are serious about water budgeting and want to measure water usage over long periods of time, he said. Rain gauges are also an effective tool to measure water usage from one irrigation event to the next.

Mecham knows that beginning the water budgeting process can be a challenge, as “people aren’t paying us to be good water managers yet.

“I walk around feeling like there’s a target on my back because I represent the irrigation and landscape industry, and past behavior and past performance sometimes merits the fact that the target is there,” Mecham said. “But this target is an opportunity to hone in and hit the bull’s-eye on how to do things better.”

Schappacher is a freelance writer based in Charlotte, N.C.

Featured Photo: ©istock.com/denisenko

About the Author:

Emily Schappacher is a freelance writer based in Cleveland.

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