Landscape irrigation can account for a significant portion of total water use for commercial, industrial, and institutional facilities. This is particularly so for facilities that maintain large lawn areas, such as golf courses, or corporate and institution campuses. There are, however, several changes in both irrigation practices and technologies that can help facility managers significantly cut back on irrigation water needs.
Simply changing irrigation watering practices can result in significant water savings. By watering lawn areas in the morning, for example, more water will reach plants and less will evaporate than watering during the middle of the day. While opinions vary, evening or nighttime watering is sometimes not recommended as mildew and other diseases may occur because plant surfaces may not dry completely. In addition, leaks are more difficult to detect with nighttime watering. Professional landscape designers can assess this risk based on plant selection.
Recent studies have also shown that commercial landscapes are typically watered at twice the rate than is necessary, providing facility managers a significant opportunity to save water by simply cutting back watering to the needs of the landscape. Irrigation technologies are now available that allow users to customize watering to apply only the amount needed. Such advanced irrigation control technologies use local weather and landscape conditions to tailor irrigation schedules to actual conditions on the site or historical weather data. Instead of irrigating according to a preset schedule, advanced irrigation controllers allow irrigation to more closely match the water requirements of plants.
Automatic controllers attached to irrigation systems can turn systems on and off and control water flow according to a pre-set time clock. Such controllers can be reprogrammed frequently during the growing season to match changing water needs from week to week. Soil moisture sensors can also be used to increase the water efficiency of irrigation systems by allowing them to operate only when irrigation is actually needed. Soil moisture sensors are placed beneath the soil surface to measure the amount of moisture in the soil and to only water when plants require water. Similarly, rainfall sensors attached to controllers can detect rainfall and prevent an irrigation system from operating if significant rainfall has occurred. Sensors are especially useful if systems cannot be monitored and adjusted regularly by managers. When operated properly, such automatic controllers can pay for themselves in reduced water usage, cost, and labor (http://www.bae.ncsu.edu/programs/extension/publicat/wqwm/ag508_6.html).
An innovative approach that uses daily weather data on evapotranspiration - the water lost due to evaporation from the soil and transpiration through plant foliage --has also been shown to be cost effective. By using a programmable timer with daily evapotranspiration data input, water use can be minimized. In fact, such water management systems have resulted in water savings of between 1,550 and 4,600 gallons per day per acre and cost savings of $1,500 to $4,500 per year per acre.
Drip irrigation, also called trickle or micro-irrigation, applies water slowly and directly to the roots of plants through small flexible pipes and flow control devices called emitters. Drip irrigation uses 30 to 50 percent less water than sprinkler irrigation and usually costs less to install. Since water is applied directly to the root zone, evaporation and runoff are minimized. Several types of drip irrigation systems can be adapted to suit a variety of applications, from watering individual trees and shrubs to beds of annuals, herbaceous perennials, ground covers, or mixed borders. Drip irrigation systems can also be operated at any time of day because foliage stays dry and evaporative water loss is not significant.
Because outdoor water use represents most summer water demand, conserving water through the use of water conserving shrubs and ground covers, called xeriscaping, can also be very effective at reducing irrigation water needs. In North Marin County, California, for example, research has shown that xeriscaping cut outdoor water by 54 percent compared to traditional landscapes. Surveys of 44 non-residential facilities (16 commercial office buildings, 12 hospitals, 9 schools, and 7 hotels) in Phoenix; Denver; Mesa, Arizona; Ventura, California; and Los Angeles found that 42 percent of water used on landscape could be conserved by xeriscaping.
Facility managers looking for opportunities to recycle and reuse water for irrigation or harvest rainwater should be aware of current regulations on this practice in Colorado. Graywater is wastewater collected from laundry operations, other process operations, showers/baths, and bathroom sinks. If properly collected and stored, it can theoretically be reused, reducing fresh water consumption for irrigation. Graywater is distinguished from "black water", which includes wastewater from toilets, kitchen sinks, and dishwashers. The Colorado Department of Public Health and Environment (CDPHE), however, does not currently separate graywater from blackwater in its regulations. Consequently, surface reuse of graywater requires permitting and monitoring. Application of graywater from systems discharging 2,000 gallons or more per day requires a permit from the CDPHE; smaller systems require permits from local health departments . Many municipalities also have connection and usage requirements that technically prohibit the use of graywater in urban areas. Similarly, larger rainwater harvesting operations that collect rainwater in cisterns for irrigation are restricted due to Colorado water law. According to the state's Division of Water Resources, in most river drainages, a person cannot divert rainwater and put it to a beneficial use without a plan for augmentation that replaces the depletions associated with diversion .
The U.S. Environmental Protection Agency (EPA) WaterSense program, which provides specifications for high efficiency plumbing fixtures, also maintains a list of landscape irrigation professionals who can assist facility managers in designing, installing, maintaining, or auditing water-efficient irrigation systems. WaterSense irrigation partners must renew their certification periodically to confirm their qualifications and demonstrate awareness of recent innovations and technology developments. The WaterSense program is also conducting research on multiple water-efficient irrigation technologies. According to the EPA, first product categories for labeling will be irrigation control technology and soil moisture sensors.
In summary, the following recommendations will help facility managers reduce the use of water in irrigation practices:
- Detect and repair all leaks in irrigation systems.
- Irrigate lawns and other landscaping during the coolest part of the day (early morning is best). During this time there is generally less wind, a lower temperature, and less sunlight, resulting in less water loss to evaporation. Avoid watering on particularly windy days when evapotranspiration can be high.
- Water trees and shrubs, which have deep root systems, longer and less frequently than shallow-rooted plants that require smaller amounts of water more often.
- Set sprinklers to water lawn or gardens only. Avoid sprinkler overlap on to streets and sidewalks.
- Instead of irrigating according to a preset schedule, consider using advanced irrigation controllers to allow irrigation to more closely match the water requirements of plants and avoid overwatering.
- Install automatic controllers on irrigation systems to turn systems on and off and control water flow according to a pre-set time clock. Reprogram controllers frequently during the growing season to match changing water needs from week to week. Install soil moisture and rainfall sensors on sprinkler systems, or consider evapotranspiration-sensing irrigation systems.
- Consider drip irrigation systems.
- Regulate pressure properly for system demands.
- Have soil tested for nutrient content and add organic matter if needed. Good soil absorbs and retains water better.
- Minimize turf areas, use native plants in landscapes, and consider xeriscaping.
- Use mulch around shrubs and garden plants to reduce evaporation from soil surfaces and cut down on weed growth.
- Remove thatch and aerate turf to encourage movement of water to root zones.
- Raise lawn mower cutting heights-longer grass blades help shade each other, cut down on evaporation, and inhibit weed growth.
- Minimize or eliminate fertilizing that requires additional watering and promotes new growth, which will also need additional watering.
- Avoid ornamental water features unless they recycle water. Use signs to indicate that water is recycled. Do not operate them during drought.