By Patricia Tripp, CFSA’s Local Produce Safety Coordinator

 

Water is a basic necessity of life and is essential in the production of fresh fruits and vegetables. Not only is water used for irrigation purposes in agriculture, but it is also often used for cleaning purposes before marketing the produce. Water may also be used to protect crops from frost or to apply fertilizers or pesticides. Ensuring that you have clean water on the farm for these practices is an important part of minimizing contamination by disease-causing microorganisms called pathogens. Water can carry pathogens such as Giardia, Cryptosporidium, Norovirus, Salmonella, and E. coli 0157:H7

 

Irrigation Water 

There are several sources of irrigation water used in agriculture. Typically, irrigation water comes from either wells or surface water sources such as ponds or streams. Municipal water can be used for irrigation, although it is not typically ideal due to associated costs. Municipal water poses the least risks for microbial contamination because it is treated and also offers the convenience of having availability to test results from the provider. Potable water (safe drinking water) is also a good choice. Surface water requires that certain precautions be taken, but can be used for irrigation.

 

Well Water

The construction of the well is crucial in minimizing potential contamination. Wells can either be drilled or bored. Bored wells are shallower than drilled wells, increasing contamination risks. They are sometimes cased with concrete and have concrete caps. Older bored wells that have not been maintained properly are particularly vulnerable to surface water that can carry pathogens through gaps in the concrete or down the outside of the good casing. Roots from shrubs or trees often create damage to wells.

 

Drilled wells are usually deeper and penetrate into hard rock, making them less vulnerable to contamination. However, all wells pose the same risks of providing a conduit for pathogens into the water supply. Wells must be well constructed and inspected at regular intervals.

 

The wellhead location is just as important as the construction of the well. Wellheads should not be located in areas that receive runoff from roads, heavy animal agriculture areas, manure storage areas, or composting areas. Do not locate wellheads within 150 feet of waste lagoons, septic tanks, or drain fields.

 

Surface Water 

Ponds and streams can be used for irrigation, with certain precautions taken. You must observe what is upstream from where water is drawn. Upstream areas that are heavily grazed or have animal access to the stream pose a higher risk of contamination.

 

Best Practices for Surface Water Irrigation 

  • Avoid using surface water following heavy rainfall until the sediments have settled and the water is clear again. Research has shown that pathogens are higher in stormwater and in sediments.
  • Use drip irrigation where practical, keeping the edible portions of the crop dry.
  • For overhead irrigation, consider irrigating early in the day and utilizing sunlight for drying, which can reduce the level of pathogens. Note: Avoid overhead irrigation of produce within two (2) weeks of the harvest to reduce your risks.
  • Exclude animals, including waterfowl and pets, from ponds used for irrigation water.
  • Standing water in the field can be a potential source of contamination, so use caution by minimizing any direct contact with the surface of the produce.

Irrigation sources and quality are directly linked to the potential for microbial contamination.

 

Rinsing Produce

Greens, root crops, and some fruits are often rinsed to remove dirt prior to marketing the product. Water used for rinsing produce must meet drinking water standards.

 

Best Practices for Rinse Water 

  • Use drinking water from a well or municipal water source for rinsing produce.
  • Never use surface water (ponds or streams) to rinse produce.
  • Test well water at least once per year and keep all test results on file.
  • Water in direct contact with produce should meet EPA maximum contaminant level goal (MCLG) microbial drinking water standards.
  • Acceptable Criteria: Generic E.coli negative test or below the detection limit and MCLG for total coliform in drinking water is zero (0).

 

Water Testing

Ensuring the safety of irrigation water can be accomplished by testing the water for the presence of pathogens. It is important to understand the types of tests available to obtain the bacteria count. There are generally three (3) different water tests available at most water testing labs: total coliform, fecal coliform, and generic E.coli (recommended for Good Agricultural Practices (GAPs) Certification). Currently, there is not one single nationwide standard for irrigation water.

 

Total coliform bacteria are microbes found in the digestive systems of warm-blooded animals, in soil, on plants, and in surface water. Fecal coliform bacteria are a kind of total coliform. The feces (or stool) and digestive systems of humans and warm-blooded animals contain millions of fecal coliform. E.coli is part of the fecal coliform group and may be tested for by itself, such as with the USDA GAPs recommended generic E.coli test. The presence of E.coli in water, in almost all cases, signals fresh fecal pollution.

 

Tests can indicate either a minimal reading of presence and/or absence or can quantify the amount of pathogens present in a given sample. These quantitative tests are what you should be looking for with the results measured in MPN (most probable number) for generic E.coli or CFU (colony forming units) for total coliform.

_________________________________________________________________________

USDA Good Agricultural Practices Standard

Clean Water Act of 1972

(Bacterial Water Quality Standards for Recreational Waters)

For water not coming in direct contact with the edible portion of a plant:

  • Acceptance Criteria: Less than or equal to 126 MPN or CFU/100mL (geometric mean of 5 samples)
  • Acceptance Criteria: Less than or equal to 576 MPN or CFU/100mL (for any single sample)

For water coming in direct contact with the edible portion of a plant:

  • Acceptance Criteria: Less than or equal to 126 MPN or CFU/100mL (rolling geometric mean n=5)
  • Acceptance Criteria: Less than or equal to 235 MPN or CFU/100mL (for any single sample)

_________________________________________________________________________

Best Practices for Water Testing 

  • Test well water at least once a year at the beginning of your growing season.
  • Test surface water more often, at least three times a year, but recommended quarterly.
  • Keep records of the water test results to document that you have managed your farm water as safely as possible.
  • If water tests indicate high levels, inspect the well for cracks or damage or check for sources of contamination in surface water. The well can be cleaned through shock chlorination.
  • Discontinue the use of the water source for irrigation purposes and test water more frequently (weekly) until results are within acceptable ranges.

 

Check with your local Extension office for information on agencies that test water in your state. Your local Extension Agent can assist with proper sample collection and will provide collection bottles. A listing of North Carolina labs can be found here.

If you have additional question regarding the safety of your irrigation water or other food safety concerns, please contact us.