Water, Water Everywhere

by Shari L. Plimpton, Ph.D.
February 2006

Water suitable for agricultural uses seems to be hard to come by these days if you read all of the reports out there about water quality for fresh fruits and vegetables. We emphasize water’s importance for fresh produce food safety through the GAP (Good Agricultural Practices) program across the country, yet we (those of us who are trying to be helpful) still seem to be generating as much confusion as we are solutions. So in this article I hope to address some of the questions I am hearing with some new information and a little perspective.

In January of this year, at the Ohio Fruit and Vegetable Grower’s Congress, we featured Dr. Trevor Suslow, Extension Research Specialist from UCDavis to speak on the topic of Water Quality and Fresh Produce Safety. Those who were able to attend heard him report on research findings that demonstrated both bacterial survival and increasing bacterial numbers at refrigerated temperatures for certain strains of infectious organisms. Clearly, this news underscores the importance of the goal of preventing microbial contamination, since our best efforts to control microbial contamination (washing and refrigeration) are not foolproof (although both are still necessary).

Recommendations published by Dr. Suslow and other researchers, and the continued reporting of foodborne illness are driving large-scale growers to adopt water quality practices that are even more diligent than those we have recommended in the GAPs program. Growers with known contamination issues are testing their water sources for fecal coliform bacteria and E. coli at least twice a month if from open sources and monthly if from closed wells. Dr. Suslow is recommending that growers who have not identified a microbial contamination issue test just as frequently for at least a year before reducing the frequency to once a year for enclosed wells and at least 3 times a season (Midwest) for open water sources.

Treatment of water to be used for agricultural purposes (irrigation, spray) is an important precaution if you hit the action threshold of 1000 fecal coliform bacteria per 100 ml and/or 126 E. coli bacteria per 100 ml. Prior to employing your treatment options, re-test for whatever microorganisms are indicated. If you are testing a well, inspect and make sure there are no opportunities for surface water to breech the well. Shocking the well with chlorine should address the problem. Retest. With an open water source, it would be necessary to add a filtration system to the water pulling from the source and follow that with an automatic chlorination system, so you can chlorinate the water for sensitive applications. Again, retest.

Using potable water is necessary in the packinghouse to avoid introducing a microbial contamination problem that did not exist coming out of the field or orchard. Since washing does not eliminate microorganisms, the goal in the packinghouse is simply to keep the water clean enough not to cause or increase microbial contamination. Repeatedly, research is showing that the most reliable method for accomplishing this is a chlorination system that is closely monitored maintaining free chlorine levels of 150 to 200 ppm.

Monitoring the free chlorine level and pH of the water on a continuous basis is simply an essential part of the process. Measuring chlorine alone gives you only half of the picture: a half that may mislead you regarding the effectiveness of the sanitation of your water. If the pH is within 6.8 to 7.2, the level of free chlorine that is in the most effective form (hypochlorous acid) is at its highest. Most of our water sources tend to run basic, so acetic acid can be used to bring the pH into range.

And why am I writing about chlorine so much and not other sanitation methods? Because, current research is not showing any other methods to be as effective for the treatment of water under agricultural conditions as is chlorination. If you are using copper ionization, please know that high levels of organic material can render it ineffective. Researchers are recommending that you supplement a copper ionization system with chlorination to improve disinfection of the water, particularly in packinghouse operations. If you are considering purchasing a copper ionization system ask the dealer to demonstrate its effectiveness in agricultural applications. A system should be able to effectively result in a five-fold reduction of fecal coliform and particularly E. coli. Ultimately, the goal is to minimize the risk and recognize the potential impact of the decisions you make regarding how to manage your water sources.

Consultation for GAPs, developing food safety programs, and passing third party audits is available through CIFT. You can reach us by calling Shari L. Plimpton at 614-314-4627 or emailing us at foodsafety@eisc.org.

Good Agricultural Practices Articles...

• ABCs of GAPs

• Cleanliness is Next to Food Safety

• The Distant Sound of Drumming

• The Efficient Use of Chlorine and Other Sanitizers in Postharvest Fruit and Vegetable Operations

• The Elements of Produce Food Safety Programs

• GAPs in Organics: Fresh Produce Safety from Pre-planting through Production

• Handling Your Food Safety Risks

• Its Not All in the Bag

• Passing a Third Party Food Safety Audit

• Pest Patrol for Fruit and Vegetable Growers

• Planning for Prevention: Fresh Produce Safety from Pre-planting through Production

• So, Just How Clean is Your Water

• Sustaining Healthy Soil

• The Value of a Food Safety Plan

• Water, Water Everywhere

• Worker Hygiene Keeps Produce Clean