Landscape Architect Articles

Water Harvesting for Landscape Contractors09-08-10 | News

Water Harvesting for Landscape Contractors

By Bruce Fordyce

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You are a landscape contractor and your client has asked you to install a water harvesting system. What do you do? How do you bid it? We asked these questions and more of top water harvesting expert John R. Bauer, President of Wahaso, Water Harvesting Solutions.

Q: A landscape contractor has been asked by a client to generate a proposal for a water-harvesting system. What is the first thing the contractor should do?
A: For a system requiring a high-quality, dependable source of irrigation water, it is probably best for the contractor to contact a company that can help match the requirements of the irrigation system with the appropriate harvesting system to capture, store, process and pressurize non-potable water. There are a number of companies in the industry now that can provide design assistance as well as systems that are preassembled and ready for installation by the contractor.

Commercial systems generally require some form of control system that can monitor system activities, send out alarms when there is an issue, and record statistics on the amount of harvested water that is available to the system or has been used during the season. Sophisticated controls can interface with the Building Automation System, send data and alerts to a web page, or provide information through interactive color touch screens in a utility or public area. The control system pictured is a custom-built Wahaso design using Allen Bradley components and a Red Lion display. Controllers range from simple controls in the $3,000 range to more complex controls with web connectivity in the $10,000 to $15,000 range.

Normally there is a final filtration step for water coming from a cistern before it is handed off to the irrigation system. Also called ''polishing,'' this step removes smaller particles that could clog emitters, and can also remove undesirable odors and colors from the water. Water from the system must then be pressurized for the irrigation system. Once again, the type and size of irrigation system will determine the flow rates and pressure needed from the harvesting system. Pumps range from simple submersible pumps supplying a few gallons per minute for a drip irrigation system to high-powered duplex pump skids with variable speed drives capable of supplying hundreds of gallons per minute to a large campus.

Q: What are the main challenges?
A: The biggest challenge is designing a system that is properly sized for a site. That requires careful analysis of supply and demand to determine the amount of storage and the capacity for filtration, sanitation and pressurization. An undersized system will use municipal water too much of the time and may not be able to supply adequate water GPM and pressure to the irrigation system. An oversized system can be prohibitively expensive.

Q: How do you design a system that will last, so you don't have to make too many maintenance calls?
A: Simplicity is a key term for a system to work as designed year after year with minimal maintenance. Complex systems tend to break down frequently or tend to be bypassed by the maintenance staff. Automated controls, self-cleaning filters and low-maintenance UV sanitation are approaches to keeping the systems simple and low-maintenance.

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Q: What trades are needed on the job?
A: This depends on the type of system being installed. Building and site engineers are usually included in the planning stages ?EUR??,,????'?????<

Q: Why should the landscape contractor be interested in learning about water harvesting?
A: We are at the beginning of a long-term trend for the use of on-site treated (''harvested'') water for landscape irrigation. There are growing shortages of fresh, potable water in many areas of the country ?EUR??,,????'?????<

The growing interest in ''green'' building is raising awareness of water supply issues and is supportive of using alternative water sources for irrigation. The LEED green certification process established by the US Green Building Council awards points in two categories for reducing the use of potable water to irrigate landscaping.

Stormwater regulations in many communities already require property owners to clean, store and detain vast quantities of stormwater, that is then slowly released to the stormwater system. Those stores of water can be accessed inexpensively to supply non-potable water to irrigation systems.

The simplest form of residential water harvesting is the rain barrel technique. This system is adequate for small landscaping needs. Shown here is a Loomis Tank Centers Rainwater Harvesting System with storage tank and first flush pipe. The system begins with a debris strainer located at the water source, whether a gutter or pipe delivery. Rainwater flows into a 'first flush' diverter that isolates the first raindrops, which contain higher amounts of contaminants. This initial rainwater can be manually disposed of or trapped in a smaller tank for use elsewhere. As the diverter is closed off, 'fresh' water is routed to the storage tanks. From here the water can be further filtered and sent to its final destination by gravity or a water pump.

The most common forms of sanitation are the addition of chlorine or the use of ultra-violet light to kill pathogens. For most irrigation systems, UV is the acceptable sanitation method as it is relatively inexpensive and maintenance free. Water from the cistern is filtered and then passes a series of UV bulbs before exiting to the irrigation system.

Q: What are the different kinds of water harvesting availabe to landscapers?
A: A water harvesting system for irrigation can run from simple to complex. The simplest system captures water from a rooftop into barrels or a small tank with a hose bib on the bottom. But large residential and commercial-grade systems require significantly more planning and equipment. They must supply large quantities of clean, safe water at predetermined pressures.

Q: What are the considerations when determining how elobrate the harvesting system should be?
A: The first consideration for any project that might use non-potable water for irrigation is the available supply and demand of water for reuse.

Q: How much water per month will the irrigation system require? What are the required gallons per minute (GPM) and pressure (PSI)?
A: What sources are available for harvesting, and at what quantities? Many systems use multiple sources of water to meet total irrigation demand.

With water supplies becoming precious and costly in many areas, landscape contractors should consider installing irrigation systems controlled by ''smart controllers'' that monitor weather conditions and irrigate based on the evapo-transpiration requirements unique to each zone in a system. These systems not only ensure that no watering takes place when rainfall has been sufficient, but can save up to 50 percent of irrigation demand by only watering as much as each plant zone requires week to week. Photo courtesy of Rain Bird

Rooftop rainwater is the most common source of harvested water for non-potable use. Supply can be determined by calculating the roof square footage and the average monthly rainfall for the area where the building is located. Supply from the rooftop of a commercial building can provide hundreds of thousands of gallons of water supply during the irrigation season.

Condensate from the building's cooling system can be a significant contributor of high-quality harvested water - especially in a large commercial building with central cooling systems. Consider harvested stormwaterfrom hard surfaces, especially for properties that already have, or plan to have, stormwater detention systems.

In areas where rain is scarce during the irrigation season, greywater may be a good source for harvesting. Greywater is ''gently used'' water from showers, sinks and washers. The biggest advantage of a greywater system is that it can provide a steady, reliable source of non-potable water throughout the year, and therefore requires significantly less storage capacity. Residential housing buildings generally offer the best opportunity for greywater harvesting.