Water has the potential to transfer plant pathogens, spoilage organisms, and human pathogens onto fruit. This section will focus on the water quality management practices that help ensure that human pathogens are not transferred onto crops as a result of water use on the farm. These same practices by-and-large limit the negative impacts of plant pathogens and spoilage microorganisms on crop output and quality.
When thinking about the food safety risk relating to microbial water quality, agriculture water can be separated into two groups: production water and postharvest water. Production water is water that contacts the harvestable portion of a crop and includes any water used for irrigation, crop sprays, or frost protection. Postharvest water is any water used during and after harvest and includes water used for washing fruit, commodity cooling, ice making, postharvest fungicides and wax applications, handwashing, and cleaning and sanitizing of food contact surfaces.
Know your Water Source. Consider the source of your agricultural water and how the water will be used in order to manage potential contamination. Here is some general information on microbial risk by water source.
- Surface water, including rivers, streams, lakes, ponds, reservoirs, and any other water source that is open to the environment, carries the highest microbial risk. Water quality from surface water can vary greatly between sites and over time. Some contamination risks include animal impacts (such as from nearby livestock operations and animal intrusion) and other users of the water system.
- Ground water, or well water, poses less risk than surface water for agricultural uses, however, hazards such as cracked well casings and leaky septic systems increase the risk that ground water can become contaminated.
- Public water supplies are monitored and treated by municipalities and therefore pose the least risk, although water still may become contaminated within your distribution system. You can obtain water quality test results from the public utility supplier.
Water Quality Standards and Risk Reduction Practices. It is important to test ground and surface water for generic E. coli (an indicator of fecal contamination) to get a measure of its microbial quality. These tests in conjunction with a risk assessment should be used to determine appropriate water use practices and risk reduction strategies.
Post-harvest water:
- Do not use untreated surface water for postharvest applications.
- Ground water used for postharvest application should have no detectable generic E. coli.
- Assess your distribution system from your source to the use point (hose nozzle) for potential contamination risks and clean out the distribution system at least annually.
Wash or Rinse Water: Small fruit crops are typically not washed as part of postharvest activities (See ‘Postharvest’ handling section). If for some reason, fruit is rinsed or washed, use single-pass water (e.g. spray from a hose, spray bar in conveyor) instead of recirculated or batch water (e.g., from a recirculating conveyor or dunk tank).
Pre-Harvest or Production Water:
- Test ground and surface water for generic E. coli (an indicator of fecal contamination) to get a measure of its microbial quality. There is currently no specific microbial standard set for pre-harvest water regardless of source. Aim to keep E. coli levels as low as possible, look for spikes and trends in test results to identify increased risks of fecal contamination, and address those risks. Use the information in conjunction with other risk assessment factors to determine appropriate use patterns.
- Conduct a risk assessment that includes information on the following factors: water system (source and nature of distribution and contamination risks), use practices, types of crop, and environmental factors (sun exposure (UV).
- Keep potentially high-risk water from contacting the harvestable portion of a crop. You can do this by switching from overhead irrigation to drip irrigation.
- Lengthen time interval between direct application of water and harvest in order to allow time for microbial die-off.
- If possible (and relevant to your farm), shift use of high-risk water from use on fruit crops to crops not typically eaten raw (e.g. sweet corn or potatoes).
It is generally recommended to test your water when you are likely to see an increase in bacterial levels and when you are using the water for agriculture activities. Late spring and summer can be a good time to test your water, since contamination with coliform bacteria (such as E. coli) is most likely to show up during wet or warmer weather. It is important to understand that the sample you collect is just a “snapshot” of the water quality and that trend information is the most helpful for making water use decisions.
In addition, it is important to follow federal and state guidelines relating to agricultural water quality standards and testing. See the ‘Produce Safety’ section for information on the Produce Safety Rule.
Water Quality Test Procedures. Follow these procedures when collecting your water sample. These steps should apply to all samples regardless of the lab used for analysis.
- Sample Location: The location of the sample will depend on whether you are trying to understand the water quality of the water source or the distribution system. Here are some general guidelines to follow for testing different water sources and the distribution system.
- Ground Water Source (Wells): Take the sample from the tap or spigot closest to the source (pump head).
- Surface Water Source: Take the water sample from a location that most accurately represents the water that is used on produce. For example, if you pump irrigation water out of a river or pond, collect the water sample as close as possible to the intake pipe located in the water source.
- Distribution System: If you use equipment that may reduce risk (e.g., a filter) or introduce risk (e.g., pipes with dead legs) or you just want to test the effect of the distribution system on the water quality, test at the end of the line (e.g., nozzle of a hose, or irrigation spigot) as well as at the source.
- Flush the line: For testing a well or somewhere along the distribution line, turn the spigot on and let the water run for at least 30 seconds or until the water sitting in the line between uses exits the system.
- Collect the sample using aseptic methods: Obtain a sterile container from the testing lab (closed and sealed). Open the container using clean hands (single use gloves can be worn for added protection), fill the container from the collection site (at least 100 ml of water), and close the container without touching the inside of the container or inside of the top. You only want to allow the sample water to touch the inside of the container. You do not want to allow microorganisms from other sources into the container.
- Put the sample on Ice: The sample must be held on ice, or otherwise maintained at below 50 °F (10 °C). Do not freeze the sample. One way to do this is to put the sample container in a sealed plastic bag and then place this bag into a larger plastic bag containing ice.
- Delivery Time: Transport the sample to the lab in under 6 hours.
Water Quality Test Labs. Use this interactive map to find lab locations in New England that will analyze your agricultural water sample. Make sure you call ahead to the lab that you are planning to use even if you have worked with this lab in the past. Confirm the following items:
- The lab tests for generic E. coli and uses an analytical method approved by the FDA for this purpose,
- Type of collection container (lab should provide sealed sterile bottle),
- Directions on sample collection, transport, and preparation (including sample documentation)
- Time from sample collection to arrival at the lab (less than 6 hours), and
- Ensure the sample can be analyzed when you drop it off.
