Tips to conserve water

Departments - Tech Solutions

Eight pointers to help you keep water use in check and grow more sustainably.

Plants grown in trough culture use about 50% less water and nutrients as compared to overhead or hose irrigation.
Photos courtesy of John Bartok

We seldom think about the amount of water that we use or its cost. For each ounce of dry matter produced by the plant, as much as two gallons of water move through the roots, stems and foliage.

As water supplies become shorter due to drought and overdevelopment, conservation becomes more important. Good system design and control can extend the water source and provide more uniform watering.

Maximum greenhouse water usage usually occurs on the hot days during the summer and is based on evapotranspiration. A “rule of thumb” is 0.3 gallon/day/sq ft of growing area. Subirrigation systems use less and pot crops use more.

Keep in mind: the water needs for your greenhouse may vary slightly depending on the crop you grow, the type of container and the local climate, but can be estimated by multiplying the square feet of growing area by 0.3 to get the amount of water that should be available.

Here are some tips to help you manage water usage this season:

Conservation is important. A good starting point is to reduce leaks. A hose or nozzle dripping at 60 drops/minute will waste 113 gallons/month. Check this frequently.

Avoid waste. Design and operate the irrigation system to limit the amount of wasted water. Avoid watering the aisles and walls. This will save on pumping cost and extend the water supply. Use anti-drip nozzles and repair any system leaks.

Boom systems provide uniform coverage while conserving water.

Design the automatic watering system for uniform coverage. The most uniform watering is achieved with flood benches, flood floors or a boom system. Drip systems do a good job if pressure compensating nozzles are used and the supply pipes are not too long. In overhead systems, the design should include double or triple overlap of nozzle patterns.

Nozzle selection should be based on the water pressure and desired irrigation rate. Select a nozzle that has a droplet size that will penetrate the foliage and minimize drift. Follow the manufacturer’s recommendation for spacing and coverage. Monitor pressure at the nozzle. Look for variations in the pattern that indicate plugging or wear. Run a cup test, which involves measuring the irrigation water caught in a series of cups laid out in a regular grid system throughout the growing area.

Maintenance can reduce energy use and prevent problems. Select pumps with premium efficiency motors. This can save up to 10% in electricity use. Check voltage at the pump, as low voltage will overheat wiring and add to the electricity use. Variable speed drive pump motors have been used, but are best for systems with multi-zones of different sizes.

Check filters. Install filters with the correct mesh for the nozzles and check frequently to see if they’re clean. Self-cleaning filters can save water and energy. Multiple filters with different mesh may be needed if the water has a lot of particulates.

Locate hot water tanks as close as possible to the largest and most frequent use. Tank and pipe insulation have a short payback. Heat water to the lowest temperature needed, usually 120° F is adequate.

Save labor with an irrigation controller. Controllers are available from one to 20 or more zones. The electronic controllers sold today are more flexible than the older mechanical timer models. Features available include easy programming, manual override of any zone, variable start and run time, activation when it is daylight, battery backup and remote control. Special controllers are available for misting, boom irrigation and locations where power is not available. A controller will operate your irrigation system when you are not available and are more accurate than hand watering.

As water supplies become shorter due to drought and overdevelopment, conservation becomes more important. Good system design and control can extend the water source and provide more uniform watering.

John is an agricultural engineer, an emeritus extension professor at the University of Connecticut and a regular contributor to Greenhouse Management. He is an author, consultant and certified technical service provider doing greenhouse energy audits for USDA grant programs in New England. jbartok@rcn.com