Contaminated agricultural water has been implicated in many foodborne outbreaks associated with fresh produce worldwide. The Food Safety Modernization Act (FSMA Produce Safety Rule) includes two types of agriculture water. The first, production water, is water used in contact with produce during growth (irrigation, fertigation, crop sprays, frost protection, cooling water, water used as mixes, etc.). The second is postharvest water, which is water used in the field during harvest as well as during packing or holding activities. FSMA requires that all agricultural water — water likely to contact covered produce or food contact surfaces — must be safe and of adequate sanitary quality for its intended use.

In this blog, we are going to talk only about production water in the FSMA Produce Safety Rule. Production water can be contaminated by human pathogens at any stage from the source to the plants, which can subsequently contaminate produce during growing stages. Therefore, understanding risks associated with production water is important to reduce risks during the production of fresh produce (fruits and vegetables). Several factors impact risks associated with production water are discussed below.

The Source of Water

There are normally three sources of production water. The first, municipal water, is normally treated and monitored to meet potable water criteria (lower risk water). However, this water may become contaminated in the piping between the treatment plant and the farm or in the water distribution system on the farm. Surface water (rivers, streams, lakes, ponds, etc.) is open to the environment. Thus, it can be considered as the riskiest source of production water, especially when it is subjected to contamination (runoff from upstream livestock operations or wastewater discharge) with microorganisms associated with feces. Pathogens often found in feces include pathogenic E. coli, Salmonella enterica serotype Typhimurium, Cryptosporidium parvum, hepatitis A, and norovirus. The third, ground/well water, is normally less likely to be contaminated with microorganisms associated with feces than surface water. Furthermore, well water filters through layers of soil, sand and rock. Therefore, the microbial load can be significantly reduced before reaching the produce. A properly constructed well can be as safe as public water supplies. However, an improperly constructed well (subjected to contamination by the environment) can have risks similar to surface waters. It is also important to mention that keeping animals (domesticated and wildlife) out of water sources is key to ensure the safety and quality of the production water as these animals can contaminate water sources with their feces.

Methods of Irrigation

The drip/trickle method reduces the direct contact of water with the produce growing above the soil, except for root crops, which significantly reduce the risk of contamination, if the water is contaminated. The overhead/sprinkler method is a higher risk method as the harvestable portions of the plants (above the soil surface) can be contaminated, if the water is contaminated, as they are directly contacted with water. Therefore, water safety and quality are critical for overhead irrigation. The furrow/flood method can be safe for irrigation, as there is less direct contact with produce above the soil than the overhead method. However, any contamination present in the water may become widely distributed across the soil and splash or soil could then contaminate the produce.

Once producers have assessed the quality of the water sources and irrigation methods, they should assess risks related to the timing of water applications. In general, more time between water application and harvest reduces produce safety risks as pathogens on produce may die off over time by ultraviolet irradiation, drying out, high temperature, low humidity, etc. However, some pathogens can survive for a long time. FSMA requires that producers subject to the rule must establish an initial microbial water quality profile (MWQP) for untreated production water sources (surface or ground water) that are applied using a direct water application method during growing.

For surface water:

• FSMA requires that the initial profile use a minimum of 20 samples taken over two years.
• After establishing the MWQP, five new samples must be analyzed each year to update the MWQP.

For ground water:

• Ground water must be tested during an initial year and annually thereafter for calculation of the MWQP.
  • Initial year: four times throughout the growing season, or over the period of a year.
  • Subsequent years: one time during the growing season or over the period of a year.

FSMA requires that generic E. coli be used as the indicator of water quality. Each source of production water must be tested to evaluate whether its MWQP meets the following criteria: 126 or less colony forming units (CFU) generic E. coli per 100 ml water geometric mean (GM) and 410 or less CFU generic E. coli per 100 ml water statistical threshold value (STV). It is important to notice that production water that does not meet the definition of agricultural water is not covered by the GM and STV criteria in the FSMA Produce Safety Rule. For example, water used for drip or furrow irrigation in apple orchards would not be considered agricultural water as long as the water does not contact the harvestable portion (apples).

Corrective Measures and Recordkeeping

FSMA requires that if the MWQP does not meet the aforementioned GM and STV criteria, producers must discontinue the use of water as soon as possible and no later than the following year unless a corrective measure is implemented. An example of corrective measures include use a microbial die-off rate of 0.5 log per day between last water application and harvest for up to four consecutive days; e.g., if the MWQP shows a GM of 1000 CFU generic E. coli per 100 ml of water. A time interval of one day with a 0.5 log per day reduction would result in a GM of 316 CFU/100 ml. A time interval of two days would result in a GM value of the water source of 100 CFU/100 ml and the water would meet the GM criterion of 126 CFU/100 ml required by FSMA. If a corrective measure of treatment is used, chemicals used to treat water must be EPA-registered. Other non-chemical treatments such as UV or filtration can be used if they meet regulatory requirements. Records for all water tests and corrective measures that are taken to identify and reduce risks of production water must be kept.