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covered produce where water is intended to, or is likely to,
contact covered produce or food contact surfaces, including
water used in growing activities (including irrigation water
applied using direct water application methods, water used
for preparing foliar crop sprays, and water used for growing
sprouts) and in harvesting, packing, and holding activities
(including water used for washing or cooling harvested
produce and water used for preventing dehydration of
covered produce) " (132). The FDA's definition is specific
and limited in scope by the regulations promulgated in the
PSR. As used here, agricultural water includes a broader
range of water activities that occur during the production
and harvest of produce crops but does not include water
use in activities performed away from the field (i.e., during
packing and holding).
In the newly proposed subpart E, the FDA also includes
a new definition for an agricultural water system, which
it defines as " a source of agricultural water, the water
distribution system, any building or structure that is part of
the water distribution system (such as a well house, pump
station, or shed), and any equipment used for application
of agricultural water to covered produce during growing,
harvesting, packing, or holding activities " (132). Agricultural
water distribution or delivery systems in produce growing
operations across the United States span the spectrum from
simple on-farm ponds or wells providing water via surface
pipe systems over a few acres to complex systems where
water is distributed to several hundred acres via a network of
above- and below-ground canals and pipes.
Within an agricultural water system, the microbial quality
of the water source has typically received more scrutiny
than have other parts of the system. Water used in produce
production and harvest activities may be surface water (e.g.,
rivers, ponds, lakes, creeks), groundwater (e.g., wells or
springs), or rainwater collected in open or closed systems
(2, 11, 19, 90, 147, 148). In some cases, groundwater may
become surface water when shallow well water breaches the
soil surface or when groundwater is pumped into reservoirs
before application to produce fields (10, 43). According to a
2015 to 2016 U.S. Department of Agriculture survey of 4,618
U.S. produce growers, 50% of growers reported using well
water for irrigation, whereas 19 and 12% used flowing and
standing surface water, respectively (4).
Agricultural water may come from on-farm sources or
may travel to a farm from irrigation water districts and/or
municipal or public water suppliers. On-farm sources include
ponds, reservoirs, wells, rivers, creeks, and streams. In some
produce-growing regions, extensive irrigation canal systems
under the management of water districts distribute agricultural
water to fields for irrigation and/or to drain excess water
from fields (16, 55, 98). Growing operations within or on
the outskirts of urban areas often receive their water supplies
from municipal sources, which are typically restricted to drip
systems when used for irrigation (55, 98). In areas where water
sources are scarce or highly regulated, agricultural water
may be supplied by private purveyors, and some water may
be delivered to fields by tanker trucks (55, 98).
Considering these diverse U.S. agricultural water sources
and systems of varying complexities, creating regulations
that effectively address the produce safety risks resulting
from microbial hazards in agricultural water is no small
task. In their proposed revisions to subpart E, the FDA
uses a risk-based approach that encompasses routine
monitoring, inspection, and maintenance of agricultural
water sources and systems and annual written assessments
of agricultural water applied directly to crops covered by the
PSR. Monitoring, inspecting, and maintaining agricultural
water systems have been essential elements of produce
growers' food safety programs for numerous years, but the
written agricultural water assessment requirement is new
for growers and has raised many questions and concerns
within the grower community and industry at large related
to effectively meeting the objective of this requirement. The
purpose of this series of review articles is to provide the
produce industry with summarized scientific information
that is pertinent to assessing microbial hazards posing a
contamination risk to agricultural water and to assist growers
in conducting agricultural water assessments. The primary
objective of this first review in the series is to document
pathogen prevalence in watersheds within produce-growing
regions and agricultural water as reported over the past
decade (2013 to 2023) and to provide growers with a
better understanding of conditions that support pathogen
persistence in water after contamination occurs.
AGRICULTURAL WATER USES
Irrigation systems are arguably the most complex component
of agricultural water systems. Many U.S. growing
operations, particularly those in western states, are in arid
and semiarid regions that are completely or partially reliant
on irrigation for crop production (10, 55, 70, 115, 124). The
U.S. Geological Survey estimated 118,131,000 gallons per
day, equaling 37% of all U.S. water use, were used to irrigate
U.S. farmland in 2015 (28).
In U.S. regions dependent on irrigation for crop production,
crops are irrigated using numerous types of systems,
including gravity systems such as furrows or flooding and
pressurized systems such as sprinklers and surface and
subsurface drip (10, 20, 35, 36, 86, 98, 115, 124). Between
1994 and 1998, irrigation systems in the United States shifted
from gravity to pressurized systems, which now make up over
two-thirds of all systems (125). Configurations of irrigation
systems vary from complex weblike networks to fingerlike
extensions attached to a main pipe, ditch, or line. Based
on water-to-crop contact, irrigation systems have varying
potential to introduce human pathogens and/or promote
human pathogen growth on unharvested crops (Table 1). For
example, microirrigation systems in an orchard are less likely
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