FSMA Produce Safety Rule and Agricultural Water Requirements

The Food Safety Modernization Act (FSMA), signed into law in 2011, fundamentally shifted the focus of food safety regulation from responding to contamination events to preventing them. For growers, one of the most consequential components of FSMA is the Produce Safety Rule, which establishes science-based standards for the safe growing, harvesting, packing, and holding of fruits and vegetables grown for human consumption.

Agricultural water is a central focus of the Produce Safety Rule because it represents one of the most significant pathways for microbial contamination of fresh produce. Water used in growing, harvesting, and post-harvest activities can introduce pathogens such as E. coli O157:H7, Salmonella, and Listeria monocytogenes if it is not adequately managed and tested.

Which Farms Are Covered

The Produce Safety Rule applies to farms that grow, harvest, pack, or hold produce covered under the rule, but several exemptions exist:

• Size-based exemption: Farms with an average annual value of produce sold during the previous three years of $25,000 or less are exempt.
• Qualified exemption: Farms with less than $500,000 in average annual food sales that sell the majority of their food directly to consumers, restaurants, or retail food establishments within the same state or within 275 miles may qualify for a modified exemption.
• Produce that is rarely consumed raw (such as potatoes destined for processing) or produce that receives commercial processing that adequately reduces pathogens may also be excluded.

Pre-Harvest vs. Post-Harvest Water

FSMA distinguishes between pre-harvest water (irrigation water applied to growing crops) and post-harvest water (water that contacts produce during or after harvest, such as wash water or cooling water). Post-harvest water standards are more stringent because direct contact with the edible portion of produce at this stage presents a higher contamination risk. Post-harvest water must meet specific microbial quality criteria and, in many cases, must contain an adequate level of antimicrobial treatment.

Recent Updates to the Agricultural Water Rule

The FDA has issued updated guidance on the agricultural water provisions, finalizing a rule in 2024 that provides growers with greater flexibility in how they assess and manage pre-harvest agricultural water risks. Rather than relying solely on numerical microbial criteria for pre-harvest water, the updated approach emphasizes systems-based agricultural water assessments. Growers are expected to conduct annual assessments of their water systems, identify conditions that could introduce hazards, and implement corrective or mitigation measures as needed. Post-harvest water requirements, however, remain largely tied to specific microbial quality standards.

What Contaminants Must Be Tested in Agricultural Water

Understanding the specific contaminants and indicator organisms that FSMA targets is essential for building an effective water testing program.

Generic E. coli as the Primary Indicator Organism

Generic E. coli serves as the primary indicator organism for assessing the microbial quality of agricultural water under FSMA. While generic E. coli itself is generally not pathogenic, its presence in water indicates fecal contamination and the potential presence of harmful pathogens. Testing for generic E. coli is preferred because it is relatively inexpensive, methodologically straightforward, and well-correlated with the risk of pathogen contamination from fecal sources.

Geometric Mean and Statistical Threshold Values

For water that directly contacts produce during or after harvest, FSMA establishes two key criteria:

• Geometric Mean (GM): The geometric mean of generic E. coli samples must not exceed 126 colony-forming units (CFU) per 100 mL.
• Statistical Threshold Value (STV): The STV, which represents the upper boundary of the water quality distribution, must not exceed 410 CFU per 100 mL.

These values are calculated from your water quality profile, which is built from multiple samples collected over time. If either threshold is exceeded, corrective actions are required before the water may continue to be used.

Salmonella and Listeria Considerations

While generic E. coli is the regulatory benchmark, many growers and buyers also test for specific pathogens. Salmonella and Listeria monocytogenes are of particular concern, especially for leafy greens, melons, sprouts, and other high-risk commodities. Retail buyers and third-party audit schemes frequently require microbial pathogen screening beyond what FSMA mandates, making pathogen-specific testing a practical necessity for many operations.

Heavy Metals and Pesticide Concerns

Agricultural water quality extends beyond microbial parameters. Irrigation water sourced from wells, canals, or surface water bodies may contain elevated levels of heavy metals (arsenic, lead, cadmium, mercury) or pesticide residues that can accumulate in soil and crops. While FSMA does not explicitly regulate these chemical contaminants in agricultural water, compliance with EPA Safe Drinking Water Act standards and buyer requirements often necessitates periodic chemical analysis of irrigation sources.

Sampling Frequency and Compliance Documentation

Building and maintaining a compliant water testing program requires consistent sampling, careful documentation, and a clear understanding of what to do when results fall outside acceptable limits.

Initial Survey Requirements

For untreated surface water sources (rivers, streams, ponds, canals), the initial microbial water quality profile requires a minimum of 20 samples collected over a period of two to four years. For untreated ground water sources, the initial survey requires a minimum of four samples collected during the growing season or over a period of one year. These initial surveys establish the baseline water quality profile from which the geometric mean and statistical threshold value are calculated.

Annual Survey Updates

Once the initial water quality profile has been established, growers must update their profiles annually. For surface water, a minimum of five new samples per year is required. These new results are combined with previous data using a rolling dataset approach, allowing the most recent data to inform the profile while older data is phased out. For ground water, at least one sample per year is required to confirm continued compliance.

Record-Keeping Requirements

FSMA requires farms to maintain records related to water testing for a minimum of two years. Records should include:

• Water source identification and description
• Sampling dates, locations, and methods
• Laboratory analytical results
• Calculated GM and STV values
• Corrective actions taken when thresholds are exceeded
• Documentation of any agricultural water assessments conducted

Corrective Actions When Standards Are Exceeded

When water quality testing reveals that the GM or STV has been exceeded, growers must take corrective action before continuing to use the water source. Options include:

• Treating the water with an approved antimicrobial agent
• Allowing time between last irrigation and harvest (die-off intervals)
• Switching to an alternative, compliant water source
• Implementing infrastructure changes to reduce contamination risk

All corrective actions must be documented and the water source must be re-tested to confirm that the issue has been resolved.

Building a Water Quality Profile

A robust water quality profile is not just a regulatory requirement but a management tool. By tracking microbial water quality over time, growers can identify seasonal trends, detect emerging contamination sources, and make informed decisions about water treatment and sourcing.

How AATLS Supports Agricultural Water Testing Programs

AATLS provides comprehensive agricultural testing services designed to help growers meet FSMA requirements efficiently and cost-effectively.

EPA-Approved Methods for E. coli Enumeration

AATLS uses EPA-approved methods for the enumeration of generic E. coli in agricultural water, including EPA Method 1603 (membrane filtration) and IDEXX Colilert/Quanti-Tray methods. These methods are specifically recognized by the FDA for FSMA compliance testing, ensuring that your results will be accepted by regulators and auditors.

Additional Agricultural Testing Capabilities

Beyond E. coli enumeration, AATLS offers a full spectrum of agricultural water and produce testing services, including:

• Salmonella, Listeria, and E. coli O157:H7 pathogen detection
• Heavy metals analysis (arsenic, lead, cadmium, mercury, and more)
• Pesticide residue screening
• General water chemistry and mineral analysis
• Soil and produce surface testing

Sampling Kits and Shipping Logistics

AATLS understands that farms are often located far from laboratory facilities. We provide pre-assembled sampling kits with sterile containers, preservatives, chain-of-custody forms, and detailed sampling instructions. Kits include pre-paid shipping labels for overnight delivery to our Tucson, Arizona laboratory, ensuring that samples arrive within required holding times.

Volume Pricing for Ongoing Monitoring Programs

FSMA compliance is not a one-time event. It requires ongoing, systematic testing throughout the growing season and across multiple years. AATLS offers volume pricing and annual monitoring agreements that reduce per-sample costs for growers who need to collect the 20 or more samples required for initial water quality profiles and the annual updates that follow.

ISO 17025 Accreditation: Results Accepted by Regulators

AATLS is ISO/IEC 17025 accredited and CDC ELITE certified. ISO 17025 accreditation is the international standard for testing and calibration laboratories, and it provides assurance that our analytical methods, quality control procedures, and data reporting meet the highest standards of technical competence. Results from an ISO 17025 accredited laboratory are accepted by the FDA, state departments of agriculture, third-party auditors, and retail buyers.

When your business depends on passing regulatory inspections and meeting buyer expectations, the accreditation status of your laboratory partner matters. AATLS delivers results you can rely on.