Make sure your irrigation source is safe

Water is the source of all life—including harmful bacteria, viruses, parasites and fungi. Although there are other sources of food contamination, and testing agricultural water doesn’t guarantee that produce will always be free of waterborne diseases, water testing is worth doing, says Will Daniels, vice president of quality, food safety and organic integrity at Natural Selection Foods, known for its brand of organic produce, Earthbound Farm.

“Water testing has always been part of our program,” Daniels says, “although the frequency changed after the 2006 E. coli outbreak.”

Photos courtesy of Natural Selection Foods.
Natural Selection Foods workers harvesting spinach work with irrigation pipe.
This shows what Natural Selection Foods goes through to prevent contamination: an employee doing a test on the harvester wears a mask, hairnet and gloves. Water jets on the product keep it cool.

Earthbound Farm began as a backyard garden in 1984. As Natural Selection Foods, it’s grown to an operation supplied by 150 independent farmers growing 40,000 acres of produce, including leafy vegetables, broccoli, celery and apples, in California, Arizona and Mexico. They sell to supermarkets, grocery stores and health food stores across the country.

Their most popular products are packaged salad mixes, which happen to be susceptible to contamination by pathogens. The leaves grow close to the ground where they easily come in contact with pathogens, the leaf surfaces can trap and hold them and the environment inside the bag is ideal for their growth. Also, the leaves are eaten raw so pathogens can’t be killed by heat.

In fact, it was packaged spinach that was identified as the cause of the E. coli O157 outbreak in 2006. After the outbreak, the company underwent a risk analysis to find out how they could enhance food safety.

“We also launched into the most comprehensive testing program in the industry,” he says. “We were pulling thousands of samples every day throughout our food safety program, from the field through finished goods, including water, soil amendments and plant tissue.”

At the request of the California Department of Food and Agriculture, Natural Selection Foods, along with other growers, shippers and processors, and university and industry scientists, looked into ways to enhance food safety. They used their findings to enhance existing good agricultural practices (GAPs), which provide general food safety guidance, and created the California Leafy Green Marketing Agreement (LGMA). Growers of almost 99 percent of the volume of California leafy greens have joined the LGMA.

LGMA is a voluntary audit program that certifies that members are complying with food safety practices for 14 leafy greens, including lettuce, spinach and cabbage. It focuses on four areas: water, workers, soil amendments and wildlife.

“Our program complies with the LGMA and goes beyond the requirements where there is opportunity to heighten some of the hurdles,” Daniels says. Natural Selection Foods also applies the procedures to sliced apples, carrots, tomatoes, melons and green onions. Testing is done at all stages by an accredited third-party lab.

Water testing gives growers the ability to catch a potential problem before it gets out of hand. It’s much less expensive, time-consuming and traumatic than dealing with a full-blown outbreak.

It isn’t possible to check every drop of water for contaminants, but random spot tests can show trends, Daniels says. For example, LGMA requires irrigation water be tested for generic E. coli, which isn’t a pathogen, but does indicate that pathogens might be present. If generic E. coli levels start increasing, growers need to determine where the problem is originating.

“Like any good program, the LGMA requires that all of these processes are documented,” Daniels says. Documentation provides historical data and also shows control of your system, which may be helpful in any type of audit or investigation.


Pathogens can lurk in everything from irrigation water, soil, compost and manure to animals, both domestic and wild, to methods of harvesting, production and transportation of the product. In terms of water sources, surface water poses the highest risk because pathogens can easily enter ponds, creeks and rivers from upstream livestock operations, wildlife and damaged sewage systems.

According to “Food Safety Begins on the Farm,” Cornell University’s booklet on GAPS, surface water should be tested quarterly in warmer climates, and three times during the growing season in cooler areas: at planting, at peak use, and at or near harvest. If results are positive, filtering the water or using settling ponds can reduce the counts.

Groundwater is less likely to be contaminated because water filters through the soil. “Food Safety Begins on the Farm” says it’s important to use water from well-built and maintained wells, and to exclude animals from recharge and pumping areas. The booklet recommends testing well water biannually and treating the water if fecal coliforms are present.

Members of LGMA are required to test irrigation water monthly for generic E. coli and to look for specific pathogens if it reaches a certain level. The irrigation water for Natural Selection Foods’ growers that comes from surface water is tested every week. They also check for salmonella, E. coli O157, enterohaemorrhagic E. coli and other pathogens.

“We look for as many as we can,” Daniels says.

The method of irrigation also affects the food safety risk. If fecal contamination exists in a given field, water can easily spread the problem. Foliar applications can spread contaminated water onto leaves, and it may not wash off, he says. Nonfoliar applications, including drip and subsurface drip irrigation, are the safest because water is filtered through the soil and contacts only the plants’ roots.

Water used on products after they leave the field, especially during washing, should also be tested regularly. Contaminated wash water can easily spread pathogens to fresh fruits and vegetables, so Natural Selection Foods tests the source of their wash water weekly. They also test the water used for processing throughout the day.

Any time contamination of a water source is detected, LGMA members are required to stop production and determine how to treat it.

“Whenever you look at sanitizing water, you have to be sensitive to the environmental effects of what you’re doing. Any water treatment option has to have minimal environmental impact,” Daniels says.

Test and hold

A problem with random spot tests is that a week or a month can pass between tests, so they don’t pinpoint the exact time the contamination began, and some contaminated produce inevitably gets through.

Natural Selection Foods’ Test and Hold program helps solve that problem. At two crucial points in the system—when salad greens arrive at the facility for processing and after they’re processed—they’re segregated and samples are tested for salmonella, E. coli O157, enterohaemorrhagic E. coli and shigella. The entire batch is held until the results return negative; if the results are positive, the batch is destroyed and production is stopped until they determine where the problem lies.

“We need to put as many hurdles in place as possible,” Daniels says. “It’s well worth it. We don’t want to ship another bag of produce that’s unhealthy.”

General GAP Guidelines

Pathogens occur naturally in soil and manure. While they can increase with improper management, some can decrease with good management. One of the advantages of using GAPS is that produce grown with less contamination is less likely to result in health hazards later on.

If irrigation water comes from surface water, know the upstream use of the water. Plant crops upstream of animal operations if possible; if not, talk to owners of upstream animal operations about the importance of keeping animals and runoff out of waterways.

Build ponds well away from apparent sources of contamination, and fence them in to prevent wildlife and domestic animals from entering. Plant a vegetative buffer to filter runoff before it gets into the water.

If water comes from a well, keep it maintained and ensure that runoff flows away from it.

Keep animals out of fields as much as possible. Compost manure and incorporate it into the soil before planting, or cover it with mulch to reduce the risk of contamination from rain or irrigation splashing the leaves. Allow at least 120 days between the application of manure and the harvesting of fruits or vegetables.

Use drip irrigation wherever possible to reduce the amount of soil and irrigation water splashing on the leaves. When using overhead irrigation, apply it early in the day so the leaves dry quickly, Daniels says. Use potable water for crop protection sprays.

“You’re talking about a universe of bacteria that’s ubiquitous, strong in numbers and evolves quickly,” he says. “When they attach themselves to leaves, they’re hard to wash off. The drier the surface, the less opportunity bacteria have to survive.”

Train workers in GAPs, provide restrooms that are clean and stocked with soap, clean water and single-use towels, and insist that everyone wash their hands before handling fruits and vegetables. Provide non-food contact jobs for sick employees.

During the harvest, keep all surfaces clean. Ensure that workers avoid standing in bins to reduce spreading pathogens with shoes, remove excess soil from produce in the field, minimize bruising and cull damaged produce to minimize the growth of pathogens.

To avoid contamination during cooling, washing and processing, use water that’s either potable or treated. Make ice with potable water. Cool produce quickly and protect from bruising and damage. Don’t overload containers or coolers. Store at appropriate temperatures to maintain quality. Keep soil, manure and animals, especially rodents and birds, out of the area.

At the end of each day, clean and sanitize all surfaces that come into contact with produce, including equipment, storage areas and sorting and packaging tables.

Clean and precool trucks before loading. Sanitize if animals were hauled, and ensure that refrigeration equipment is working properly.

The author is a freelance writer based in Altadena, Calif., and a frequent contributor to Growing.