November 2020
According to the USGS, agriculture is one of the largest consumers of water resources in Nevada with about 70% of all water withdrawals going to irrigation. The majority of that water is going to animal feed crops, but the State’s fruit and vegetable farms also depend on irrigation from surface and groundwater.
This article focuses on managing the quality of water on produce farms to ensure that it does not become a vector for foodborne illness. If pathogens such as E. coli and Salmonella in water contaminate produce that is bound for market, both public health and the longevity of the farm can be at risk. All water that contacts fruit and vegetables during the growing season is considered 'agricultural water’ under the Produce Safety Rule (note this only applies to produce that is typically eaten raw). This can include water for irrigation, fertigation, foliar sprays, frost protection, cooling, and produce washing. Below is an overview of the best practices for managing agricultural water systems, key resources for testing water, and options for correcting water quality issues. We compiled these with the small to medium Nevada produce grower in mind, and included tips from our own experience here at DFI.
Key On-Farm Practices and Resources:
1. First, identify all types and uses of agricultural water on the farm – this decision tree can help. Consider mapping sources of water and the distribution system as part of your food safety plan, including backflow preventers and any treatment devices. DFI identified the need for additional backflow prevention (preventing water from flowing the wrong direction and carrying pathogens into the water system) through an exercise like this.
2. Select water application methods and timing that reduces direct contact with the edible portion of crops. Here in the high desert, drip irrigation is an efficient choice for vegetables and fruit in any case. Where flood or overhead irrigation are in use, the timing of application can be planned to reduce risks (see discussion of pathogen die-off rates in 5. below).
3. Inspect the water system regularly for leaks, cracks in wellheads, broken emitters and any other pathways for pathogens into the system. Be aware of adjacent land uses and activities that could introduce contamination, such as surface water runoff from uphill livestock. Jot down a schedule for this inspection and record observations. DFI does this informally when running irrigation and more formally at the beginning and end of the warm season.
4. Test water to establish a baseline. Farms must be able to show that their water meets Produce Safety Rule standards by certain deadlines ranging from 2022 to 2024, depending on a farm’s annual produce sales. Farms using municipal water only need to keep a copy of test results from their supplier (DFI keeps TMWA records on file). Testing requirements for groundwater and surface water vary, based on risk, as follows.
| Water source |
Testing requirement |
| Untreated surface water (pond, river, ditch, etc.) – highest risk water sources |
20 samples in first year and 5 samples every year thereafter |
| Groundwater (well) |
4 samples in first year and 1 sample every year thereafter |
|
Municipal water
|
Keep copy of annual utility test results |
NDA has compiled testing criteria and a list of labs in the region that provide these water testing services; here also is a link to labs nationwide. The cost for testing one water sample for total coliform and/or E. coli is $25-50 in Nevada. Contact DFI for guidance on sampling (where, how, when) and check out the Western Center for Food Safety at UC Davis for online tools that help to interpret test results.
5. What should you do if testing reveals contamination or your system is visibly compromised based on your inspection? Issues will be handled most easily if there is an advance plan for corrective actions. For example, the farm could have a backup plan to switch to an alternative safe water source while making water system repairs. Also, understanding how to calculate pathogen die-off in advance will be useful – this is basically how to determine an adequate waiting period between harvest and the last application of the water you are concerned about. Find out how via the Western Center for Food Safety.
There are also water treatment options for handling ongoing water quality issues, including chemical treatment such as chlorine (follow the EPA label for all chemicals) and non-chemical treatment such as filters, UV light or ozonators. Added benefits of valid treatments are that you will not need to do water quality testing (as described in 4.) and your water system may become more efficient (less clogging!). Contact DFI for assistance with validating and verifying treatment methods to meet Produce Safety Rule requirements.
6. Post harvest water (any water used during and after harvest) must meet stricter standards under the Produce Safety Rule – no detectable generic E. coli in 100 mL of water. The same testing regimen is required for this water (as described in 4.). Farms often use sanitizers when submerging fruit and vegetables in wash water. Although such treatment is not required, it can help maintain water quality and reduce the risk of cross-contamination (spread of pathogens among produce through the water). Always follow the EPA label for sanitizers. DFI prioritizes single pass spraying of produce or not washing produce at all to avoid risks introduced by dunking vegetables. When we do use the sinks, we use Sanidate 5.0 (a common hydrogen peroxide and peroxyacetic acid sanitizer that is more stable than chlorine and OMRI approved) and monitor temperature and turbidity.
7. Keep records of the farm’s water quality test results, verification of water treatment, and/or management actions. This can be as simple as a file folder and a notebook. Find record-keeping guidance and templates here.
It’s best to develop a comprehensive food safety plan for the farm and designate someone to oversee its implementation. Need assistance with produce safety planning or best practices for ag water? Contact DFI for a free call or visit, and check out additional resources below.
Resources:
Buchanan, J.R., Chapin, T.D., Danyluk, M.D., Gunter, C.C., Strawn, L.K., Wszelaki, A.L., Critzer, F.J. 2019. Bridging the GAPS: Approaches for Treating Water On-Farm. Curriculum V1.0.
Cornell University. 2020. National Good Agricultural Practices Program: Agricultural Water for Production (accessed November 2020).
Cornell University. 2019. Produce Safety Alliance Grower Training, Modules 5-1 and 5-2 (accessed November 2020).
Western Center for Food Safety. 2020. Real-World Solutions to Food Safety Challenges (accessed November 2020).
