Food Safety Plan – Water Source & Use (WSU5-SOP)
Water Sampling SOP (for water that contacts crops during GROWING)
Policy Purpose
Type farm/business name here performs water sample testing on a scheduled basis to detect any
potential or existing contamination on all water sources including well, ditch, canal, pond, reservoir,
river and reclaimed water. This SOP refers to water that contacts crops during growing. This SOP
does not include requirements for sprouts.
For water used in any manner that contacts produce during/after harvest (for example, water
applied to produce for washing or cooling, used to prevent dehydration before cooling, used to make
ice that directly contacts produce, used on food contact surfaces or used for washing hands during
and after harvest activities), refer to the Crop Handling (CH) section.
Laboratory test results and any corrective actions are recorded. This SOP includes employee training
for water sample collection, water sampling schedule, sampling method, the logging activities and
requirements, water sample result requirements, understanding water sample results and
calculations, corrective actions, and activities that may lead to audit failure.
Procedures
Employee Training for WSU5-SOP and WSU5-Log
Document employee training in the employee training log (FSP2- Primary Training Log).
Water Sampling Schedule
Water sample testing is scheduled throughout the year, especially throughout the growing season
prior to harvest by trained employees. Document water testing schedule in the Farm Plan Calendar
(Calendar). Water sample testing frequency depends on the type of water source (i.e. surface or
ground water). There are no requirements to test:
 Municipal or public water as long as testing results from the facility are kept
 From any water that has been treated using an EPA-approved method
If untreated SURFACE or GROUND water is used, you must use the following testing schedules and
requirements:
Testing schedule for untreated SURFACE water samples
The FDA requires:
1. Initial survey (2-4 year process)
All food safety policies and procedures should be developed using national, state and local guidelines. Information presented in these on-farm food safety materials was
compiled from reputable sources, such as USDA-FSIS, FDA and the Food Safety Modernization Act final rules. The information is provided for educational purposes only and
should not be considered legal advice. Therefore, no responsibility is assumed or implied by CSU, Chico Research Foundation or CSU, Chico.
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Revision Date: July 24, 2016
Food Safety Plan – Water Source & Use (WSU5-SOP)
 Collect a minimum of 20 samples, as close to harvest as possible over 2-4 years
2. Annual survey
 Collect a minimum of 5 samples each year
Testing schedule for untreated GROUND water samples
The FDA requires:
1. Initial survey (1 year process)
 Collect a minimum of 4 samples, as close to harvest as possible over 1 year
2. Annual survey
 Collect a minimum of 1 sample per year
Water Sampling Method
1. Organize supplies
 Most contract labs will provide a 100 mL sterile container with a snap or screwcapped lid for sampling
 Label the bottle with:
 Location where water sample was collected using Growing Area Map (Map)
 Date of sample collection
 Time of sample collection
 Initials of the person taking the sample
2. Water source preparation
 If you are collecting from a spigot or shunt valve, turn on water to the highest flow
possible for four minutes and then turn it off
 Wipe the inside of the spigot or valve opening with a 10% bleach solution and let sit
for one minute before collecting the sample
3. Taking water sample(s)
 If you are collecting samples from multiple places like different wells, spigots, valves,
etc. make sure that you wash your hands and use gloves before collecting each
sample to avoid contamination
 Turn the water to a moderate, steady flow
 Keep the container closed until the sample is ready to prevent dust, soil, or other
debris from contacting the sample container
 Do not touch the underside of the bottle lid, the bottle lip, or inside of the bottle
 Do not rinse the bottle before filling
 Look for the fill-line or a 100 milliliter mark
 It is important to fill the bottle past this line for an accurate sample analysis
 If the bottle does not have a mark or instructions, fill the bottle to the top
 Replace the lid and wipe the outside of the container with a clean paper towel
All food safety policies and procedures should be developed using national, state and local guidelines. Information presented in these on-farm food safety materials was
compiled from reputable sources, such as USDA-FSIS, FDA and the Food Safety Modernization Act final rules. The information is provided for educational purposes only and
should not be considered legal advice. Therefore, no responsibility is assumed or implied by CSU, Chico Research Foundation or CSU, Chico.
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Revision Date: July 24, 2016
Food Safety Plan – Water Source & Use (WSU5-SOP)
4. Transporting sample(s)
 The sample(s) should be placed on ice/cooler immediately after collection
 Samples should be received by the contract lab within 24 hours of collection or
according to their directions, whichever is earlier
 Samples should be tested for generic E. coli or for what your buyers/regulators require
Water Sample Logging Activities
Use the WSU5-Log to record water sample test results and corrective actions. Testing calculations
will fill-in automatically. Use Growing Area Map (Map) to record water sample collection location.
The following tables are provided in the WSU5-Log:
Table 1: Initial SURFACE water sample results (complete 20 samples over first 2-4 years)
Table 2: Ongoing SURFACE water sample results (complete 5 additional samples each year)
Table 3: Initial GROUND water sample results (complete 4 samples over first year)
Table 4: Ongoing GROUND water sample results (complete 1 additional sample each year)
Table 5: Microbial Die-off Rate method used when inspection, treatment & retesting does not occur
Before the initial GM and STV for SURFACE water can be calculated, collect 20 samples over 2-4
years and complete Table 1. After the initial GM and STV have been completed in Table 1, collect 5
new samples each year to recalculate the GM and STV for SURFACE water in Table 2.
Before the initial GM and STV for GROUND water can be calculated, collect 4 samples over 1 year
and complete Table 3. After the initial GM and STV have been completed in Table 3, collect 1 new
sample each year to recalculate the GM and STV for GROUND water in Table 4.
Water Sample Result Requirements
Water testing results must follow two requirements:
1. Geometric Mean (GM) must be <126 MPN or CFUs of generic E.coli per 100 mL of water.
2. Statistical Threshold Value (STV) must be <410 MPN or CFUs of generic E.coli in 100 mL of water.
Understanding Water Sample Results and Calculations
What is Most Probable Number (MPN) or Colony Forming Units (CFUs)?
The water sample test results will be provided by the lab as Most Probable Number (MPN) or Colony
Forming Units (CFUs). These two types of units essentially provide the same information and quantify
or measure how much bacteria is in the water sample. The MPN or CFUs results, provided by the lab,
need to be less than (<) the maximum acceptable FDA requirements.
All food safety policies and procedures should be developed using national, state and local guidelines. Information presented in these on-farm food safety materials was
compiled from reputable sources, such as USDA-FSIS, FDA and the Food Safety Modernization Act final rules. The information is provided for educational purposes only and
should not be considered legal advice. Therefore, no responsibility is assumed or implied by CSU, Chico Research Foundation or CSU, Chico.
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Revision Date: July 24, 2016
Food Safety Plan – Water Source & Use (WSU5-SOP)
What is a Geometric Mean (GM)?
The Geometric Mean (GM) is the average test results. See Appendix A below for details.
What is Statistical Threshold Value (STV)?
The Statistical Threshold Value (STV) indicates the consistency of the sample test results. See
Appendix A below for details.
Remember, once the water sample results are entered, the GM and STV will automatically be
calculated for you.
Notes about test results:
1. If a result provided by the lab contains a “<” symbol (i.e. <2, <1 or <0.5), use one half of that
value for the test result in the log. For example, if a result provided by the lab is <1, use 0.5
for the test result column.
2. If your test result is so high that there is a “>”symbol, such as >2419.6, then there was either
excessively dangerous amounts of microbial contamination or a mistake could have been
made in the lab or during sample collection. In this case, take one of the three corrective
actions listed in the Corrective Action section below, take a new sample and retest.
Examples of Tables 1-4 for tracking SURFACE and GROUND water sample results are found on the
following pages below:
Table 1: Initial SURFACE water sample results (complete 20 samples over first 2-4 years)

Page 5
Table 2: Ongoing SURFACE water sample results (complete 5 additional samples each year)

Page 6
Table 3: Initial GROUND water sample results (complete 4 samples over first year)

Page 7
Table 4: Ongoing GROUND water sample results (complete 1 additional sample each year)

Page 7
All food safety policies and procedures should be developed using national, state and local guidelines. Information presented in these on-farm food safety materials was
compiled from reputable sources, such as USDA-FSIS, FDA and the Food Safety Modernization Act final rules. The information is provided for educational purposes only and
should not be considered legal advice. Therefore, no responsibility is assumed or implied by CSU, Chico Research Foundation or CSU, Chico.
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Revision Date: July 24, 2016
Food Safety Plan – Water Source & Use (WSU5-SOP)
Example Table 1: Initial SURFACE water sample results (complete 20 samples over first 2-4 years).
D at e of
s am pl e
c ol l ec t i on
Ti m e of
s am pl e
c ol l ec t i on
St af f who
c ol l ec t ed
s am pl e
Tes t
res u l t s
8/1/17
2:00 PM
Smith
106.6
9/1/17
2:00 PM
Smith
325.5
10/1/17
9:30 AM
Smith
387.8
11/1/17
7:30 AM
Jones
435.2
12/1/17
10:45 AM
Smith
313.0
1/1/18
2:00 PM
Smith
128.1
2/1/18
9:30 AM
Smith
124.6
3/1/18
7:30 AM
Smith
46.4
4/1/18
10:45 AM
Jones
69.5
5/1/18
2:00 PM
Jones
60.5
6/1/18
9:30 AM
Smith
43.2
7/1/18
7:30 AM
Smith
41.7
8/1/18
10:45 AM
Smith
40.6
9/1/18
2:00 PM
Jones
39.7
10/1/18
9:30 AM
Smith
39.8
11/1/18
7:30 AM
Smith
410.6
12/1/18
10:45 AM
Smith
387.3
2/1/19
2:00 PM
Jones
307.6
5/1/19
9:30 AM
Smith
115.3
8/1/19
7:30 AM
Smith
146.7
G eom et ri c
M ean ( G M ) *
St at i s t i c al
Thres hol d
Val u e ( STV) *
122
399
Com m en t s an d/or
Correc t i ve Ac t i on s
*The GM and STV for SURFACE water are calculated by using the most recent 20 water samples. The GM requirement for sample test results cannot exceed 126 MPN or CFUs of generic E.coli per 100
mL of water. The STV cannot exceed 410 MPN or CFUs of generic E.coli in 100 mL of water.
All food safety policies and procedures should be developed using national, state and local guidelines. Information presented in these on-farm food safety materials was
compiled from reputable sources, such as USDA-FSIS, FDA and the Food Safety Modernization Act final rules. The information is provided for educational purposes only and
should not be considered legal advice. Therefore, no responsibility is assumed or implied by CSU, Chico Research Foundation or CSU, Chico.
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Revision Date: July 24, 2016
Food Safety Plan – Water Source & Use (WSU5-SOP)
Example Table 2. Ongoing SURFACE water sample results (complete 5 additional samples each year). Use table 2 for every new year.
Tes t
res u l t s
Dat e of
s am pl e
c ol l ec t i on
Ti m e of
s am pl e
c ol l ec t i on
St af f who
c ol l ec t ed
s am pl e
9/1/17
2:00 PM
Smith
325.5
10/1/17
9:30 AM
Smith
387.8
11/10/17
7:30 AM
Jones
435.2
12/1/17
10:45 AM
Smith
313.0
1/1/18
2:00 PM
Smith
128.1
2/1/18
9:30 AM
Smith
124.6
3/1/18
7:30 AM
Smith
46.4
4/1/18
10:45 AM
Jones
69.5
5/1/18
2:00 PM
Jones
60.5
6/1/18
9:30 AM
Smith
43.2
7/1/18
7:30 AM
Smith
41.7
8/1/18
10:45 AM
Smith
40.6
Use last 19 result s
Geom et ri c
M ean ( GM ) *
St at i s t i c al
Thres hol d
Val u e ( STV) *
124
405
f rom previous yr
9/1/18
2:00 PM
Jones
39.7
10/1/18
9:30 AM
Smith
39.8
11/1/18
7:30 AM
Smith
410.6
12/1/18
10:45 AM
Smith
387.3
2/1/19
2:00 PM
Jones
307.6
5/1/19
9:30 AM
Smith
115.3
8/1/19
7:30 AM
Smith
146.7
10/1/19
10:45 AM
Smith
141.4
1/10/2021
12:30 PM
Smith
155.1
119
377
4/1/20
12:45 PM
Smith
164.8
114
344
7/1/20
1:45 PM
Smith
135.3
108
301
Com m en t s an d/or
Correc t i ve Ac t i on s
1/1/20 test result =
501.2 MPN. GM above
126 MPN. STV above
410 MPN. Stopped using
water. Inspected water
system, cow broke
through fence and fixed
fence. Retest on
1/10/20. GM and STV
recalculated and water
safe to use.
*The GM and STV for SURFACE water are calculated by using the most recent 20 water samples. The GM requirement for sample test results cannot exceed 126 MPN or CFUs of generic E.coli per 100
mL of water. The STV cannot exceed 410 MPN or CFUs of generic E.coli in 100 mL of water.
All food safety policies and procedures should be developed using national, state and local guidelines. Information presented in these on-farm food safety materials was
compiled from reputable sources, such as USDA-FSIS, FDA and the Food Safety Modernization Act final rules. The information is provided for educational purposes only and
should not be considered legal advice. Therefore, no responsibility is assumed or implied by CSU, Chico Research Foundation or CSU, Chico.
6
Revision Date: July 24, 2016
Food Safety Plan – Water Source & Use (WSU5-SOP)
Example Table 3. Initial GROUND water sample results (complete 4 samples over first year).
Dat e of
s ampl e
c ol l ec t i on
1/1/17
Ti me of
s ampl e
c ol l ec t i on
2:00 PM
St af f who
c ol l ec t ed
s ampl e
Smith
4/1/17
9:30 AM
Smith
122.3
7/1/17
7:30 AM
Jones
95.9
10/1/17
10:45 AM
Smith
101.0
Tes t
res u l t s
Geomet ri c
M ean ( GM ) *
St at i s t i c al
Thres hol d
Val u e ( STV) *
106
121
Commen t s an d/or
Correc t i ve Ac t i on s
106.6
*The GM and STV for GROUND water are calculated by using the most recent 4 water samples. The GM requirement for sample test results cannot exceed 126 MPN or CFUs of generic E.coli per 100
mL of water. The STV cannot exceed 410 MPN or CFUs of generic E.coli in 100 mL of water.
Example Table 4. Ongoing GROUND water sample results (complete 1 additional sample each year). Use table 4 for every new year.
Tes t
res u l t s
D at e of
s am pl e
c ol l ec t i on
Ti m e of
s am pl e
c ol l ec t i on
St af f who
c ol l ec t ed
s am pl e
4/1/17
9:30 AM
Smith
123.4
7/1/17
7:30 AM
Jones
121.0
10/1/17
10:45 AM
Smith
125.0
1/1/18
1:00 PM
Smith
Use last 3 result s
G eom et ri c
M ean ( G M ) *
f rom previous yr
524.7
177
St at i s t i c al
Thres hol d
Val u e ( STV) *
Com m en t s an d/or
Correc t i ve Ac t i on s
448
1/1/18 test result =
524.7 MPN. GM above
126 MPN. Calculated
die-off using Table 5 in
WSU5-Log and stopped
using water for 1 day
between irrigation and
harvest. No retest
needed because used
die-off method.
*The GM and STV for GROUND water are calculated by using the most recent 4 water samples. The GM requirement for sample test results cannot exceed 126 MPN or CFUs of generic E.coli per 100
mL of water. The STV cannot exceed 410 MPN or CFUs of generic E.coli in 100 mL of water.
Corrective Actions
If the water does not meet these criteria, corrective actions are required as soon as possible.
There are 3 corrective action options:
1. Re-inspect the water, remove any identifiable hazards and retest the water (a lab test will
usually take 24 hours)
2. Follow the Microbial Die-off Rate method in Table 5 of the WSU5-Log. This method allows
time for potentially dangerous microbes to die-off on the field from sunlight and changes in
moisture, temperature, pH, etc. between last irrigation and harvest. The maximum number of
days you need to wait using this method is 4 consecutive days.
o Microbial die-off and appropriate waiting period between the last day of irrigation and
when produce is safe to harvest can be calculated automatically using Table 5 in
WSU5-log. Enter the GM and STV values in the boxes for Day 1 and the die-off will
automatically be calculated for days 1-4.
All food safety policies and procedures should be developed using national, state and local guidelines. Information presented in these on-farm food safety materials was
compiled from reputable sources, such as USDA-FSIS, FDA and the Food Safety Modernization Act final rules. The information is provided for educational purposes only and
should not be considered legal advice. Therefore, no responsibility is assumed or implied by CSU, Chico Research Foundation or CSU, Chico.
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Revision Date: July 24, 2016
Food Safety Plan – Water Source & Use (WSU5-SOP)
o The appropriate waiting period (i.e. number of days) between irrigation and harvest is
determined by the results in these die-off columns. The waiting period depends on
when both the:
1. GM is < 126 MPN or CFUs of generic E.coli per 100 mL of water
2. STV is < 410 MPN or CFUs of generic E.coli per 100 mL of water
Example Table 5. Microbial Die-off Rate method used when inspection, treatment & retesting does not occur.*
Geomet ri c
M ean ( GM )
GM Di e-of f
( goal < 126 M P N
or CFUs ) **
St at i s t i c al
Thres hol d
Val u e ( STV)
STV Di e-of f
( goal < 410 M P N
or CFUs ) **
Day 1
177
53
448
135
Day 2
53
16
135
41
Day 3
16
5
41
12
5
1
12
4
Wai t i n g
P eri od
Day 4***
*Complete this table if GM from Tables 1-4 is > 126 MPN or CFUs and/or STV > 410 MPN or CFUs.
**The appropriate waiting period (i.e. number of days) between irrigation and harvest is determined by the results in these die-off columns. The
waiting period depends on when the GM is < 126 MPN or CFUs of generic E.coli per 100 mL of water and when the STV is < 410 MPN or CFUs of
generic E.coli per 100 mL of water.
*** Maximum waiting period necessary between the last day of irrigation and the day of harvest.
o See Appendix A below for detailed explanation of Microbial Die-off Rate method.
3. Treating (i.e. chlorination) the water (See WSU6-SOP and WSU6-Log)
Audit Failure
Audit failure will occur if:
1. GM is >126 MPN or CFUs of generic E. coli per 100 mL of water or STV is >410 MPN or CFUs
of generic E. coli per 100 mL of water and no corrective action was performed.
2. Irrigation water sample tests are not conducted as indicated in the Water Sample Schedule
section above for EACH water source (per FSMA).
3. Presence of E coli O157:H7 and/or salmonella found in water currently being used can result
in automatic audit failure by a third party auditor.
All food safety policies and procedures should be developed using national, state and local guidelines. Information presented in these on-farm food safety materials was
compiled from reputable sources, such as USDA-FSIS, FDA and the Food Safety Modernization Act final rules. The information is provided for educational purposes only and
should not be considered legal advice. Therefore, no responsibility is assumed or implied by CSU, Chico Research Foundation or CSU, Chico.
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Revision Date: July 24, 2016
Food Safety Plan – Water Source & Use (WSU5-SOP)
Appendix A
Geometric Mean (GM) Calculation Formula Used
=GEOMEAN(Sample 1:Sample 20)
Statistical Threshold Value (STV) Calculation Formula Used
=EXP((1.282*(STDEV.S(ln(Sample 1):ln(Sample 20))))+(AVERAGE(ln(Sample 1):ln(Sample 20))))
Details on Microbial Die-off Rate Calculation Method
Microbial die-off or log reduction like a “0.5-log reduction” refers to amount of the bacteria that has
died-off or been reduced each day. Here are 2 examples:
1. If your water samples have a GM value of 177 MPN or CFUs and STV value of 448 MPN or CFUs,
you do not meet the requirements for the GM of < 126 MPN or CFUs or the STV of < 410 MPN or
CFUs. Using a microbial reduction rate of 0.5 log per day:
 For GM:
o Day 1 (-log0.5)*177 = 53 MPN or CFUs (safe)
o Day 2 (-log0.5)*53 = 16 MPN or CFUs (safe)
o Day 3 (-log0.5)*16 = 5 MPN or CFUs (safe)
o Day 4 (-log0.5)*5 = 1 MPN or CFUs (safe)
 For STV:
o Day 1 (-log0.5)*448 = 135 MPN or CFUs (safe)
o Day 2 (-log0.5)*135 = 41 MPN or CFUs (safe)
o Day 3 (-log0.5)*41 =12 MPN or CFUs (safe)
o Day 4 (-log0.5)*12 = 4 MPN or CFUs (safe)
 Therefore, a 1 day waiting period is sufficient to assume the produce is safe to harvest.
Geomet ri c
M ean ( GM )
GM Di e-of f
( goal < 126 M P N
or CFUs ) **
St at i s t i c al
Thres hol d
Val u e ( STV)
STV Di e-of f
( goal < 410 M P N
or CFUs ) **
Day 1
177
53
448
135
Day 2
53
16
135
41
Day 3
16
5
41
12
5
1
12
4
Wai t i n g
P eri od
Day 4***
2. If your water samples have a GM value of 1,790 MPN or CFUs and a STV value of 2,236 MPN or
CFUs, you do not meet the requirements for the GM of < 126 MPN or CFUs or the STV of < 410
MPN or CFUs. Using a microbial reduction rate of 0.5 log per day:
 For GM:
o Day 1 (-log0.5)*1790 = 539 MPN or CFUs
o Day 2 (-log0.5)*539 = 162 MPN or CFUs
All food safety policies and procedures should be developed using national, state and local guidelines. Information presented in these on-farm food safety materials was
compiled from reputable sources, such as USDA-FSIS, FDA and the Food Safety Modernization Act final rules. The information is provided for educational purposes only and
should not be considered legal advice. Therefore, no responsibility is assumed or implied by CSU, Chico Research Foundation or CSU, Chico.
9
Revision Date: July 24, 2016
Food Safety Plan – Water Source & Use (WSU5-SOP)


o Day 3 (-log0.5)*162 = 49 MPN or CFUs (safe)
o Day 4 (-log0.5)*49= 15 MPN or CFUs (safe)
For STV:
o Day 1 (-log0.5)*2236= 673 MPN or CFUs
o Day 2 (-log0.5)*673 = 203 MPN or CFUs (STV is <410, but GM too high on Day 2)
o Day 3 (-log0.5)*203 = 61 MPN or CFUs (safe)
o Day 4 (-log0.5)*61= 18 MPN or CFUs (safe)
Therefore, a 3 day waiting period is sufficient to assume the produce is safe to harvest.
Geomet ri c
M ean ( GM )
GM Di e-of f
( goal < 126 M P N
or CFUs ) **
St at i s t i c al
Thres hol d
Val u e ( STV)
STV Di e-of f
( goal < 410
M P N or
Day 1
1790
539
2236
673
Day 2
539
162
673
203
Day 3
162
49
203
61
Day 4***
49
15
61
18
Wai t i n g
P eri od
Microbial Die-off Rate Calculation Formula Used
=-LOG10(0.5)*GM
=-LOG10(0.5)*STV
All food safety policies and procedures should be developed using national, state and local guidelines. Information presented in these on-farm food safety materials was
compiled from reputable sources, such as USDA-FSIS, FDA and the Food Safety Modernization Act final rules. The information is provided for educational purposes only and
should not be considered legal advice. Therefore, no responsibility is assumed or implied by CSU, Chico Research Foundation or CSU, Chico.
10
Revision Date: July 24, 2016