Flooding and food safety on farms

The U.S. Food and Drug Administration defines flooding as the flowing or overflowing of a field with water outside a grower’s control. This can result from an overflowing water body such as a river, lake, or a stream. Rainwater that pools in some parts of the field is not considered flooding. 

Flooding can pause risks to public health because the flood water can be contaminated with harmful microorganisms such as Salmonella and E. coli, as well as heavy metals, and chemicals. Research shows that soil (sandy clay), irrigation water, and leafy green vegetables that come in contact with flood water can become contaminated with high levels of foodborne pathogens, and that these pathogens can be detected in samples for more than two weeks. Growing fields that are adjacent to livestock farms stand a higher risk of contamination in case of a flood because of animal feces that may be present on these farms and dragged to other places by flood water. The tips below can help reduce food safety risks related to flooding of crop fields.

Before the flood 

• If you know the history of the field, then do not grow food in fields prone to flooding.
  • If you learn about flooding that will happen soon, then you can prepare by
    • Managing (emptying, relocating) portable toilets.
    • Removing chemicals and equipment from places where flood water is likely to go.
    • Harvesting any food crops that may be ready to harvest.

After the flood

• Evaluate if food has contacted flood water. Impacted food cannot be fed to humans. Discard food crops that have contacted flood water.
  • Equipment and tools that contacted flood water should be cleaned and sanitized before using them in areas that were not flooded.
  • Wait for the flood water to drain. Do not work the soil while water is present. Equipment may get stuck, and soil will become compacted.
  • Wear personal protective equipment (PPE) when working in areas that just flooded and dispose it off or clean and sanitize PPE after use.
  • Wait to replant fields for 30-60 days to allow time for water to drain and for microorganisms to die. Research suggests that high solar radiations (between 6 and 8 MJ/m2) following a flood event can contribute to microbial die off such that E. coli levels in irrigation water and soil reduce significantly within 3 weeks after the flood.
  • Encourage faster draining and drying of the soil for faster microbial die off. This can be done by turning the soil.
  • If resources allow, test the soil for the level of contamination with foodborne pathogens and indicator microorganisms (Salmonella, Generic E. coli). Testing results can shorten the waiting time. You can follow these sampling and testing instructions and metrics.
  • Wells and surface water sources located in or near an area that was flooded should be tested for contamination before the water is used for any food or cleaning related activities.
  • Allow a buffer area of 30 feet from where flood water had collected to adjacent areas. This space allows you to turn equipment as you move in and out of the field and to prevent contamination of non-flooded areas.
  • Document the flooding event. Include areas affected, how you responded, and write a plan to follow if fields happen to flood again.

References and resources 

Microbial safety considerations of flooding in primary production of leafy greens: A case study.

Sampling and testing instructions for flooded soils 

Food Safety for flooded fruit and vegetable fields.

FDA Guidance for Industry: Evaluating the Safety of Flood-affected Food Crops for Human Consumption