Production water includes any water that contacts fresh produce before harvest. This includes water used for irrigation, application of foliar sprays, and in-field cooling or frost protection. Agricultural water used to grow fresh produce can carry and distribute human pathogens. Surface water is more likely to be contaminated by human and animal fecal material than ground water because it is open to the environment. Therefore, use of surface water for production can pose a greater risk to produce safety compared with ground water or municipal water. Surface water used for fresh fruit and vegetable production has been found to be contaminated with human pathogens such as Salmonella, Escherichia coli O157:H7, Giardia, and Cryptosporidium (1-4). Water distribution systems are also a concern, because these systems distribute water throughout the farm and can become contaminated if pipes, backflow prevention devices, or other pieces of the distribution system are not in good condition and functioning properly. Understanding the risks associated with production water use and how to minimize them are important for produce safety.
Actions can be taken on the farm to reduce the risks of contamination from agricultural water used during the production of fresh produce.
- Map and inspect all water sources and distribution systems (5).
- Select water application methods that reduce risks by reducing direct contact with the harvestable portion of the crop.
- Test agricultural water for quantified generic E. coli.
- Identify a water testing laboratory (6).
- Collect the sample using aseptic technique (7).
- Deliver samples to the laboratory within the required time (7).
- Keep records of all test results as well as water management actions (8).
Map and Inspect All Water Sources and Distribution Systems
A map of all water sources and distribution systems can be useful to identify how water moves throughout the farm. Inspect agricultural water sources, such as surface water and wells, at the beginning of the growing season and periodically throughout the season (5). As part of this inspection, assess surface water sources such as ponds, lakes, rivers, reservoirs, and canals to determine if wildlife or adjacent land uses pose any contamination risk. Well casings should be inspected to make sure they are intact and well recharge areas should be inspected to make sure no risks are present. Take action to reduce risks, based on inspection observations, before the water is used for fresh produce production (e.g., repairing broken equipment, reducing animal access to the water, treating the water, or using filtration to remove contaminants from the water).
Inspect water distribution systems, as well as equipment used to move water, at the beginning of the growing season and continue to monitor during the growing season to ensure the lines are clear and not likely to introduce microbial risks to the crop receiving the water (5). This includes repairing broken lines and emitters as well as removing any debris in the lines, such as nesting wildlife, which could lead to contamination. Repairing damaged equipment is very important because faulty water emitters can turn a drip system into an overhead system, with water spray in direct contact with the harvestable portion of the crop.
Water should be drained from the pipe between irrigation applications because, if bacterial pathogens are present in the irrigation water and the water sits stagnant in the pipe between irrigation applications in warm weather, bacterial pathogens can multiply in the pipe and potentially become incorporated into a biofilm.
Select Water Application Methods that Reduce Risks
Drip irrigation is the least risky method of water distribution because the water normally does not contact the harvestable portion of the crop, unless you are growing root vegetables or the drip line malfunctions. Overhead irrigation and the application of foliar crop sprays result in direct water contact with the harvestable portion of most crops, so safety is influenced by the quality of water that is applied. If you are using a surface water source for overhead irrigation or for mixing sprays, test this water before using it by sampling throughout the production season and having it analyzed for generic E. coli as described in the next section about testing.
If you have concerns about the quality of your water that comes in direct contact with the crop, there are other actions that can be taken to reduce microbial risks. In addition to testing to understand the quality of your water, you can also:
- Apply any water that contacts the harvestable portion of the crop using a time interval before harvest, to allow drying and exposure to UV from sunlight. Time can reduce levels of potential pathogens on the crop. The longer the time interval between application of water and harvest, the more risk reduction is possible.
- Treat the water to improve water quality, either with chemical (according to label) or physical (such as filtration) treatment.
- Use water application methods that do not result in direct contact with the harvestable portion of the crop, such as drip or trickle irrigation.
Test Agricultural Water for Generic E. coli using a Quantitative Method
Water that directly contacts the harvestable portion of the plant is most relevant to food safety because water can carry pathogens and contaminate the crop. Water that directly contacts the harvestable portion of the crop should be tested for generic E. coli using a quantitative method (9). This means the test will indicate the amount of E. coli in the sample, not just if E. coli is present or absent. Testing for generic E. coli is not the same as testing for total coliforms or fecal coliforms (two different water quality tests), so be sure to ask specifically for analysis of generic E. coli using a quantitative method.
The only way to know the quality of untreated water is to test the water. Consider testing all water used on the farm, even though some water (like water that is delivered through drip lines to above-ground crops) might not have to meet the same quality criteria as water that directly contacts the harvestable portion of the crop. Keep in mind that some buyers and audit schemes have quality criteria even for water that does not directly contact the harvestable portion of the crop. Understanding water quality allows growers to make informed water management decisions, especially once typical levels are understood after sampling over several seasons (10, 11).
Identify a Water Testing Laboratory
The water samples collected from the farm need to be analyzed for quantified generic E. coli. To have this analysis done, find a laboratory that is capable of providing the analysis (6). The current industry standard is to test for generic E. coli with a quantitative method. E. coli is the specified indicator organism included in the FSMA Produce Safety Rule (PSR) (9). A variety of analysis methods are used at different labs and different regulations or buyers may impose specific requirements. Confirm with the lab that the method they use meets your needs (12). Also be sure to specify the type of water source, since many labs focus on potable (drinking) water and are not prepared to handle quantitative analysis of samples from surface water sources.
Sample Collection and Delivery
Follow the sampling and delivery guidelines provided by the laboratory doing the water analysis. It is a good idea to confirm that the laboratory guidelines are consistent with any regulatory requirements (7). Sampling and delivery guidelines will include using designated sampling containers (sterile, enough volume), sampling methods (aseptic technique), keeping the sample chilled once collected (refrigeration temperature, not frozen), and delivery times (generally less than 6 hours from collection, thought overnight express shipping may be acceptable). Please review the sample SOP in this portfolio for basic sampling instructions.
Keep Records of All Water Management Actions and Test Results
Keep records for all water tests as well as any water management actions that are taken to identify and reduce risks that may be present in the water or the water delivery system (8). Template logs are provided in this document to assist you with this recordkeeping process.