So, Just How Clean is Your Water?

by Shari L. Plimpton, Ph.D.
June 2005

As we work through another year of helping growers with the application of Good Agricultural Practices (GAPs) to their fresh produce operations, I am repeatedly reminded of just how important, and potentially confusing, is the issue of water quality. First of all, we emphasize in our education programs that water quality is one of the most critical control points for minimizing the risk of foodborne illness. Of course, water contamination of any kind: chemical or microbiological is to be avoided both out in the field and in the packing house. In the GAPs program we provide recommendations based on good, general science yet, we emphasize that no standards have been established for fresh produce. Ultimately we end up applying the standards for potable water and wait for the research to tell us if we have any other options or considerations.

I have written before about the standards for water testing and treatment of wells and will repeat just a few words about it here. Anyone who has heard me speak, has heard about testing wells annually and open water sources quarterly for fecal coliform and E. coli. During farm consultations we provide Standard Operating Procedures (SOPs) that give growers methods for solving a contamination problem whether it’s for water intended for use out in the field, or for water used in the packing house. Those SOPs generally rely heavily on the use of chlorine (in its variety of forms) to treat the water, killing bacteria present in the water and, depending on the level of free chlorine in the water, killing some bacteria on the surface of produce being washed.

And yet the world is a changing place, new problems pop up, and, if we are lucky, new solutions present themselves as well. Some growers are using sanitizers other than chlorine to solve a number of problems inherent to using chlorine (fumes, corrosion, discharge issues, to name a few). Some of the methods I have seen more commonly employed in the Midwest are copper ionization, and hydrogen peroxide or hydrogen dioxide.

Copper Ionization is an electrical method that generates electrically charged copper ions into a water system. These ions are reactive and are thereby capable of inactivating bacteria, mold, mildew and similar microorganisms. The level of copper used by these automatic systems is not toxic and copper has been effectively used to generally control disease in other applications. The effectiveness of copper ionization on certain spore-forming bacteria and parasites is questionable when it is not monitored or controlled properly. All systems should have a method for being able to monitor the copper ion level in the water. Combination with another sanitizer (i.e. chlorine, hydrogen peroxide, etc.) is a way to cover all of your bases, yet maintaining lower levels of reactive oxidizing sanitizers.

Using hydrogen peroxide or hydrogen dioxide is another acceptable method for achieving water sanitation. Here, we are taking a form hydrogen and oxygen molecules that are highly reactive, bringing them into contact with organic material (bacteria), and (at a high enough level) effectively killing bacteria, parasites and inactivating viruses. One big plus of using these compounds is that the by-products of their reactions are water and oxygen. There is no need to be concerned about fumes or water discharge; however, these are reactive materials and should be handled carefully. Again, monitoring the level of the reactive components is critical to maintaining control over your sanitizing system.

Of course these are only two alternative sanitation methods for water treatment of many. Regardless of the one you choose, the most common error I find is that there is no monitoring system for the water sanitation system. With chlorine, people are accustomed to using test strips to measure the free chlorine levels. If they combine this measurement with monitoring the pH of the water, they can be sure to maintain the right balance in the water to achieve inactivation of microorganisms. A pH that is either too high or too low will result in the chlorine moving into a form that will not be effective for killing microorganisms. And if you simply dump and don’t measure, you may just be throwing money down the drain.

Using an ORP system to monitor the effectiveness of your water treatment system may be a more useful and easy method to assure that your treatment system is working for you on a consistent basis. ORP stands for Oxidation-reduction potential. An ORP system is a system that can measure the oxidation-reduction potential (in terms of milli-volts (mV)) of the treated water. Research has shown (Trevor V. Suslow, Ph.D., UCDavis, Pub. 8149, 2004) that a reading of 650-700 mV will result in the killing of pathogenic bacteria within 30 seconds. Advantages of this system can be automated dosing based on system readings, automatic recording of measurements (helpful for those who face third-party audits), and reduction of the need to test the water for pH.

Maintaining backup methods with which to calibrate your ORP system is strongly recommended. Ultimately you should know as much about your water chemistry (pH, mV, free ion levels) as you probably know about the soil chemistry of your fields. Failing to monitor is a failure to control. Water systems that are out of control are at a much greater risk for being the source of a foodborne outbreak. Minimize your risk and measure.

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