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Using surface water on the farm during drought conditions?

Annalisa Hultberg, Extension Educator, food safety

Many regions of the state have continued to be in moderate to severe drought this season, which is impacting water tables and wells. Are you making changes on your farm because of a dropping water table, like using pond or river water for irrigation? Learn more about using surface water for irrigation, if this is something you are doing or considering doing.

This farm pond has become a water source for deer and racoons in the drought. 
You can see the tracks from animals on the banks of the pond. Using pond water like 
this for irrigation is a risk due to the high potential for pathogens in the water from wildlife and other sources of contamination.

What are the risks with surface water sources?

Surface waters like ponds are considered a high risk water source since their quality can be highly variable and they are susceptible to contamination from animals and other sources of fecal contamination. This water is much more likely to contain pathogenic E. coli and Salmonella than well water sources.

Surface water sources are vulnerable to microbiological risks from surface and sub-surface sources of fecal contamination. Some risks include:

  • Livestock feces if livestock have access to the water
  • Birds and duck feces
  • Leaking septic tanks
  • Humans recreating
  • Runoff from nearby fields, livestock and roadways
  • Dead animals
  • Dumping and trash
Testing pond water for bacterial contamination

While surface water can be used for irrigation in the field with caution, surface water should never be used for postharvest uses like washing vegetables, washing hands, or sanitizing and cleaning surfaces. Use only well or municipal water that has been tested to show no detectable generic E. coli for postharvest uses. 

If using surface water like ponds or streams for irrigation, the following practices can reduce the potential for contamination of your fresh produce

  • Take steps to reduce contact of the water with the edible portions of the crop, such as by using drip tape under plastic. This has the added advantage of using less water than overhead, and also reduces plant disease and mildew that can come with continually wetting plant foliage. Water applied with overhead irrigation is more likely to touch the edible portion. 

  • Test the water for bacterial contamination to understand the baseline bacterial load. Know that this level will change rapidly, however, as surface water is open to the environment. It is recommended that surface water sources be tested multiple times per season, since they are so variable. For more info on testing click here.

  • Apply surface water sources to produce that is not likely to be eaten raw. For example, potatoes, winter squash and beets. If there is contamination in the water, the cooking will likely serve as a "kill step" to reduce potential contamination if it gets on the produce.

  • Allow a "die off" period between application of the surface water and harvest of the produce. Bacterial die-off levels in water are highly variable, and the number of days required for adequate die-off varies greatly depending on the initial level of contamination of the water, the crops, the UV and wind conditions, and other field conditions. For this reason, relying on die-off alone to reduce bacterial levels in water is not a good strategy. 

  • The FSMA rule allows 4 days from water application to harvest to use water that does not meet initial standards, meaning it has high contamination levels. This assumes a 0.5 log die-off per day.  
Livestock in an irrigation pond
Photo: Wes Kline, Rutgers University

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