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. 

The quality of water used when applying pesticides can impact pesticide efficacy. For example, organic matter in water can bind with some pesticides or clog nozzles.  The pH of the water in your tank mix can also affect the efficacy of some pesticides. Insecticides, in particular, have a tendency to break down (hydrolyze) rapidly in alkaline water. Water pH can vary, depending on the source, from 5 to 9.5. Neutral water has a pH of 7, while alkaline water is higher than 7. If your water pH is much higher than 8, you may want to consider using an acidifying agent such as vinegar to lower the pH in the tank. Many of the pH-sensitive pesticides have acidifying agents in the formulation that moderate the effect of alkaline water. However, growers who suspect a pH problem should have their water tested. This can be done on the farm with pH test kits.

There is considerable public concern about water quality, and agriculture is coming under increasing scrutiny regarding practices that can affect water quality. 

Pesticide and Fertilizer Impact on Water Quality

Many pesticides and fertilizers are soluble in water and can leach through the soil to contaminate underlying groundwater. Several factors affect the movement of chemicals in the soil and their likelihood of reaching groundwater. Consideration of these factors can minimize the threat to groundwater.

Adsorption is the binding of a chemical to the surfaces of soil particles and organic matter. Some chemicals are tightly adsorbed and do not easily leach from soils.

Persistence refers to the amount of time a chemical will stay in the environment before being broken down into nontoxic substances. The rate of breakdown is affected by sunlight, temperature, soil pH, moisture and microbial activity. Pesticide persistence is measured in terms of half-life which is the length of time needed for one-half of the amount applied to break down. Persistent chemicals break down slowly, increasing the chance for them to leach from the soil. Conversely, short-lived materials may be degraded before significant leaching occurs. Many pesticides are broken down by sunlight (photodegradation) and/or microbial action. Incorporation of pesticides into the soil reduces or eliminates photodegradation. As depth in the soil increases, there is less microbial degradation. Any practice that slows degradation increases persistence and the likelihood of leaching. Generally, foliar applied materials are more likely to break down before significant leaching occurs than those that are applied to the soil.

Pesticide Characteristics: Solubility is very important in the leaching of a pesticide. Chemicals that are highly soluble in water are easily leached as water moves downward. If practical, use the least soluble material at the lowest effective rate.

Soil Characteristics: Soil texture and organic matter greatly influence the movement of pesticides and fertilizers. Fine-textured soils and those with high amounts of organic matter are highly adsorptive, whereas sandy soils low in organic matter are not. Highly permeable soils with permeable underlying layers allow for rapid downward movement of water and dissolved chemicals. Know your soils and apply chemicals accordingly.

Water Table: High water tables are especially vulnerable to contamination because little time is required for chemicals to reach groundwater.

Fertilizers: Nitrogen (N) in the nitrate form is highly soluble, persistent and not adsorbed to soil particles. Nitrate N is not only leachable but is recognized as a health threat at concentrations above 10 ppm in drinking water. Infants are most susceptible to nitrate in drinking water. The ammonium form of N is adsorbed by soil particles and is less subject to leaching. However, ammonium N is converted to nitrate N in the soil, and this can occur quite rapidly. Note that urea, a common form of fertilizer N, is converted in the soil to ammonium and then to nitrate.

Appropriate management practices can reduce the likelihood of nitrate leaching. Any time large amounts of N are applied, significant leaching can occur if there is heavy rain. By applying some of the needed N at planting and the rest during one or more topdressings, you can avoid having large amounts of nitrate present at any one time. Not only can this reduce leaching, it can improve production by providing N during periods of greatest crop uptake.

Nitrogen left over in the soil at the end of the season is highly subject to leaching. A cover crop should be planted to take up unused N. The N will again become available for future crops as the cover crop breaks down.

Postharvest Water Discharge

Discharge of wash pack area water is regulated differently in each state. Wash water may be of variable microbial quality and also may contain antimicrobial pesticides (sanitizers for cleaning and sanitizing or in produce wash water).  Consider the area around your wash and pack shed (or outside area) and think about where it would be appropriate to discharge wash water.  Direct discharge away from food crop production areas, avoid areas with human or vehicle traffic, and do not discharge directly into any bodies of water. Be sure to check with your local and state regulatory authorities to ensure your water discharge plan is appropriate. If you are using antimicrobial pesticides, follow the label directions for water discharge (many labels do not contain this information).