Water Testing for Produce Food Safety and Third-Party Audits, DPHS Lab Agrees to Do Testing

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Water testing for microbial indicators is a recommended Good Agricultural Practice (GAP) for irrigation water and Good Handling Practice (GHP) for packing house water and is part of a produce food safety plan. It is a common requirement of third party GAP and GHP audits.

Water testing should be done yearly. For wells used in packing houses, samples should be taken just prior to the packing season. For irrigation wells, samples should be taken at the beginning of the irrigation period. For irrigation using surface water (ponds, streams, rivers, ditches), it is recommended that water be tested at the beginning of the irrigation period and just prior to first harvest.

For all sources, water should be tested for generic E. coli, the indicator bacteria for fecal contamination of water. For irrigation water, test should be done in a way to quantify bacterial levels (numbers of bacteria in the sample).

For packing houses, the water should be potable (same as drinking water) and should have no E. coli.

For irrigation water, current guidelines are that the samples where water will contact the harvested part of the vegetable or fruit should be less than 126 CFU (colony forming units) or MPN (most probable number of bacteria) per a 100 ml sample. For crops where there will be no foliar contact the sample should be less than 576 CFU (or MPN)/100 ml. Sources over these levels should be evaluated for sources of fecal contamination (livestock, wildlife, sewage).

A MOU (memorandum of understanding) is being finalized between the Fruit and Vegetable Growers Association of Delaware and the Delaware Public Health Service Laboratory to do water testing for Delaware produce growers. For wells with potable water where presence or absence of E. coli needs to be tested, the cost will be $2.00 per sample. For irrigation sources where numbers of E. coli need to be determined, the test will be $18.00 per sample. Details of the program are being worked out and the program should be up and running within 4 weeks.

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