Active water harvesting involves using mechanical systems to collect, filter, store and recycle rainwater, stormwater, cooling system condensate and “greywater”—water that has already been gently used for the purposes of hand-washing, showering, bathing, dishwashing or laundry. These four types of non-potable water are proactively collected through the use of containment systems located above or below ground level. Active water harvesting systems include the tanks, piping, metering, pumps and other infrastructure elements needed to store, treat and transmit this collected water for beneficial use. These systems may be gravity-flow-based or pump-based depending on the size and needs of the site.

While collecting water through passive means is relatively simple, it does offer less control over how much water is collected, stored and applied to the landscape. An active harvesting system can often provide a complete supply of water for landscape irrigation, supplementing it with municipal water if necessary. Actively harvesting water requires more forethought, planning and monitoring than passive collection, along with a larger initial investment in systems and materials, but it can also provide a greater return.

5 Steps for Success
Before jumping into the design, construction and implementation of an irrigation system fed by water harvested on site, it’s important to gain a firm understanding of a project’s needs, current situation, budget and desired end result. Following these five steps can ensure the development of solid plans that result in the best possible outcomes.

Step 1: Determine the reasons why the site wants to harvest water.
Knowing why you want to harvest water is necessary for a positive end result. For example, a developer who wants to earn LEED certification for a new office complex will need to abide by certain design and implementation standards during the process that the manager of a shopping center who wants to reduce utility bills will not. Obviously, there may be a combination of reasons involved. Understanding the motivation to harvest water can help developers and owners work successfully with specifiers and architects to design systems that satisfy needs both now and in the future.

Step 2: Estimate how much water will be needed for landscape irrigation.
At sites with existing irrigation systems, it’s possible to analyze past water bills for a fairly accurate estimate of landscape irrigation water use, taking seasonal fluctuations and system efficiency into account. For new landscapes and structures still in the planning or construction phases, this estimate will depend greatly upon the types of plants, shrubs, trees and turf chosen for the site. For an accurate estimate of the amount of water a site will need for landscape irrigation, determine answers to the following questions:

• For new sites, what will the landscaped area be in square feet?
• What types of plantings (turf, shrubs, flowers) are present or planned for the site and where are they located?
• What’s the prevalent soil type at the site—clay, loam or sand?
• What types of technology will most efficiently irrigate the site—overhead sprays and rotors, drip or subsurface?
• How many irrigation stations (zones) will there be?
• How many GPM (gallons per minute) will the irrigation system require and at what pressure level?
• How many gallons of water will the system require per month?
• Will the irrigation system be supplemented with municipal water if the harvested water supply is inadequate or runs dry?

Step 3: Establish and quantify renewable water resources at the site.
It’s tempting to try to collect every possible drop of rainwater or greywater, but it may not be economically feasible. If a building is still in the design stage, it’s far easier to plan ahead for the appropriate pipes and fixtures than it is to retrofit existing plumbing. Be realistic about how much water a site can reclaim for irrigation purposes by answering the following questions:

• What is the average rainfall experienced at the building’s location?
• What is the current or planned design and square footage of the building’s roof? What percentage of it could receive collectible rainwater?
• Does the site’s cooling system generate condensate that could be harvested? If so, how much?
• Is there or will there be a sump pump that can generate groundwater for reuse?
• If the plan is to harvest greywater from inside the facility, how much are its occupants expected to generate through the use of sinks, showers, washers or other sources?

Step 4: Designing the water harvesting system
After determining how much water is needed for irrigation and the prospective sources of that water, it’s time to work with a water harvesting specialist to design the system. Design considerations include storage type and location, equipment location, local regulatory issues and system controls and reporting capabilities.

Storage:
Many factors play into the decision of whether to store water above ground or underground. Some buildings may have an architectural style that’s not conducive to visible cisterns or tanks. Water stored above ground is also susceptible to freezing in cold climates, and it can be difficult to reserve enough physical space on the property for large steel or polyethylene tanks. Conversely, while storing water underground does offer protection against freezing, property owners must bear the costs of excavation to make way for the tanks or vaults. Water stored below ground is also subject to a greater risk of infiltration, and in some regions, high water tables may make it difficult or impossible to have large, subsurface tanks.

Equipment Location:
Finding an appropriate location to house any pumps needed to move the water from its storage tanks to the irrigation system—as well as sterilize, dye or chlorinate it, if local regulations require—is another design consideration. If the building lacks indoor storage, this equipment can be placed inside a weatherproof housing located outside the main structure. In either case, the types and sizes of the necessary mechanical equipment will depend on the amount of water needing to be moved, local regulatory issues and the desired water pressure.

Controls:
Sophisticated water harvesting systems often include a computerized, touch-screen controller that monitors the status of mechanical components, water levels in each storage tank and the total amount of water harvested by the system on a periodic basis (often monthly). In many cases, an optional interface can enable Web-based control for convenient access from any computer with an Internet connection.

When water is being harvested for irrigation, it’s also possible to integrate smart, or weather-based, irrigation control like for a complete package. For example, Rain Bird’s ESP-LX Series Controllers with the optional ET Manager Cartridge can enable harvested water to be used as efficiently as possible, taking details such as evapotranspiration, effective rainfall, temperature and humidity into account. When managing multiple irrigation sites, central control software like Rain Bird’s Maxicom^2® or IQ v2.0 offers both convenience and flexibility. In the case of one, large, contiguous irrigation site, Rain Bird’s IQ v2.0 or Site Control software provides a good solution. These types of programs not only offer the ability to schedule irrigation from a remote location, but they can also provide features such as advanced reporting, flow monitoring, lighting system control and automated ET management.

Consider these questions when determining the appropriate level of control for any water harvesting system:

• Who is in charge of irrigation management and maintenance, and where are these individuals located—on-site or off-site?
• How many sites must be managed, and how large are they?
• If reports are required, how often must they be generated and what type of data must they include?
• Will smart irrigation controls be incorporated into the water harvesting system or will irrigation control be kept separate?

Step 5: Evaluating or designing the irrigation system
Non-potable water supplied to irrigation systems must be kept completely separate from a site’s drinking water source. Many municipalities also require that irrigation systems be designed to prevent “ponding” of non-potable water to avoid overspray into public areas. If a harvested water supply will be supplemented with a municipal water source for irrigation, a backflow prevention valve must be installed on the potable water service into the building to prevent cross-contamination between harvested water and potable water. Some municipalities require that a licensed plumber install the backflow prevention valve; others allow irrigation contractors to perform the installation.

Spray heads, valves and pipes intended for use with reclaimed water are identifiable by their purple color. Local ordinances will dictate any need to retrofit existing systems with these purple components. In some cases, rather than replacing components with those specifically intended for non-potable water, existing system components must only be marked with tags identifying them as such.

If a business or organization takes the time, effort and expense to install a water harvesting system, its irrigation system should be as efficient as possible. Today’s irrigation technology uses less water than ever before, making now the perfect time to audit and retrofit an existing system or install a highly-efficient new system. In addition to smart controllers and central controls, soil moisture sensors and rain sensors, like Rain Bird’s SMRT-Y Soil Moisture Sensor Kit and WR2 Rain/Freeze Sensor can make any system more efficient. The SMRT-Y measures the actual moisture present in the soil and relays that reading back to the controller for what’s called “closed-loop irrigation.” With user-controlled thresholds for rainfall and temperature, the WR2 prevents unnecessary watering.

It’s also important to specify rotors and sprays that use matched precipitation rates and pressure regulation for optimum coverage and water-efficiency. Rain Bird’s 5000, 5500 and 8005 Series Rotors all offer Rain Curtain™ technology for larger, wind-resistant water droplets and superior close-in watering with optional pressure regulation. Nozzles with check valves can reduce wasteful water seepage from rotors or spray heads located near the bottom of a hill or slope. Rotary nozzles are an excellent choice for sloped areas or clay soil, as they apply water at a lower precipitation rate that allows it to be absorbed rather than run off. When appropriate, drip irrigation and subsurface irrigation can be up to 70 percent more efficient than overhead sprays.

The future of water harvesting
Water harvesting is not simply a trend that will quickly come and go. It’s likely that future water shortages both in the United States and internationally will continue, making it necessary for all of us to reduce the amount of potable water we use for irrigation. Harvesting rainwater, stormwater, cooling system condensate and greywater is a smart and relatively painless process that can conserve significant amounts of fresh water for drinking. Using these unconventional sources of water responsibly while also incorporating today’s water-efficient irrigation technology is the best way to continue maintaining beautiful, healthy landscapes with little impact on the world’s fresh water supply.