Water Resources

CU-14-700

Interpreting Irrigation Water Quality Reports

Dara M. Park, Sarah A. White, L.B. McCarty and Nick Menchyk

Water Chemistry Testing Water Sources

What? Water is not just H2O? What else could Knowing what is in your irrigation water can help in
possibly be in there? As water evaporates, it managing your landscape. Far too often, an irrigation
condenses in the atmosphere and falls as rain; it water test is used as a diagnostic tool after plants are
flows overland, seeps through the soil, and moves exhibiting some type of stress. However, irrigation
underground. During this cycling, it is processed by water tests should be done when the irrigation system
humans, animals, plants, and microbes, picking up is installed and with some frequency, dependent on the
some compounds, leaving some behind, and acting as outcome of the initial test, location (are you near the
a medium to form new ones. coast?), and the potential for fluctuations in water source
quality.
Mineralogy and weathering influence water chemistry.
Water can dissolve minerals in rocks. Chemicals Use opaque plastic containers to collect your water
may be released (dissolved) into water as microbes sample. Rinse out the bottle three times with the water
decompose organic material. Plants exude chemicals you will be sampling before bottling the final sample.
from their roots to increase availability of minerals in Place your name, location, and date on the sample bottle
soil pore water. Further, extreme temperatures cause with a permanent marker. Place in a cooler or refrigerator
water to expand in rocks breaking them apart and until delivery to the laboratory. Make sure to submit
releasing minerals that were once tightly bound. the sample within 24 hours of collection. Clemson
University’s Agricultural Service Laboratory (CU-ASL)
Humans impact water quality in various ways. has a specific set of tests for evaluating irrigation water
Nutrient, pathogenic, and pharmaceutical waste <http://www.clemson.edu/public/regulatory/ag_svc_lab/
can be introduced from treated and untreated irrigation_water/index.html>.
sewage. Metal and chemical waste can be released
as by-products of industry and mining operations.
Fungicides, herbicides, and pesticides are applied for What’s In Your Irrigation Water
agricultural purposes. Urbanization and development Table 1 discusses the components of water that CU-ASL
expose subsoils that are naturally anaerobic, introduce tests for in relation to irrigation of plants, not for drinking
deicing rock salts, and change landscape use. water or for livestock health. If you have further questions
contact your county extension agent <http://www.
Some water sources are influenced more by man- clemson.edu/extension/county/index.html>.
made actions than natural processes. For example,
reclaimed stormwater runoff and treated (reclaimed)
wastewater are increasingly common irrigation water Other Information that can be
sources as demand for potable water increases. Determined from the Analysis
Besides comparing your reported values with those in
Table 1 to evaluate your irrigation water, you can make
other water quality conclusions by using the values for
other calculations:
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Interpreting irrigation water quality reports

Table 1. Irrigation water component, its severity range, description of issue, and strategy for managing the problem.

Severity
Component Origin Not a Increasing Severe Issue Management
Problem Problem Problem
Runoff to water bodies can Reverse osmosis.
Ground & surface
Phosphate cause algal blooms followed by
waters, fertilizers,
(PO43--P) < 1.2 1.2 - 2.4 > 2.4 a decrease in dissolved oxygen, Fertilizer amounts & scheduling
landscape runoff, &
ppm ultimately resulting in less should account for amount
treated sewage.
aquatic life. contributed by irrigation water.
Potassium Increase K in plant tissues, can
Dissolved rock, salts, > 50 for Distillation, reverse osmosis, or
(K+) < 20 ppm 20 - 50 lead to limited plant uptake of
soil, & fertilizers. foliar† ion exchange methods.
ppm other required nutrients.
< 20 25 – 250 > 250 soil
Water softeners are most
Calcium Dissolved rock, & water ion Binds with CO32- and HCO3- to
commonly used.
(Ca2+) limestone, gypsum, hazard form lime deposits, contributes
ppm salts, soil, & fertilizers. < 60 60 - 80 > 100 foliar to “hard water” & salinity. Can use other ion exchange
injury† methods.
Magnesium Dissolved rock, Binds with CO32- and HCO3- to
Water softeners & ion exchange
(Mg2+) limestone, dolomite, < 25 ppm 25 - 35 > 35 form lime deposits, contributes
methods.
ppm salts, soil, & fertilizers. to “hard water” & salinity.
Source dependent:
Not usually a problem, can give
Occurs naturally in small 1- reverse osmosis.
water a milky appearance.
Zinc amounts. 2- other ion exchange methods.
(Zn) < 2.0 ppm > 2.0 3- distillation.
Zinc released from corrosion of
ppm May result from
plumbing systems (copper-zinc
industrial pollution. Increase pH of water using
alloys), with low pH water.
sodium carbonate (soda ash).
Occurs naturally in Not usually a problem, staining
Copper small amounts, also & corrosion possible (see Zn).
Increase pH using sodium
(Cu) from mining operations, < 0.2 ppm 0.2 – 5.0 > 5.0
carbonate.
ppm acidic water, & from Toxicity in some plants at
corroding copper pipes. concentrations >1.0 ppm.
Not usually a problem.
Dissolved from shale, & Precipitation then filtration.
sandstone.
Manganese Excessive Mn
At low concentrations use a
(Mn2+) < 0.2 ppm >0.2 1- turns water grayish/black.

CU-2014-700
Present in flooded soils water softener.
ppm 2- can coat leaf surfaces
& wetlands with low
& subsequently reduce Keep soil pH between 6.0 –
dissolved oxygen.
photosynthesis. 7.0, with good drainage.
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Interpreting irrigation water quality reports

Table 1 cotinued. Irrigation water component, its severity range, description of issue, and strategy for managing the problem.

Severity
Component Origin Not a Increasing Severe Issue Management
Problem Problem Problem
Iron treatment depends on the
Rust forms in the presence of
type of problem.
oxygen (in water or air).
If salt present, metal will rust Common techniques include:
Iron is dissolved from faster. Rust causes reddish- 1- aeration then sediment
underlying rocks & soil. brown staining and/or flake filtration.
Iron
off and clog nozzles, filters, 2- sediment filtration then a
(Fe2+ or Fe3+) < 0.3 ppm 0.3 - 5 >5
Can be present if low and lines. Iron complexes with water softener (caution:
ppm
pH water passes through organic materials & bacteria these usually use sodium).
iron pipes or equipment. causing slimes. 3- precipitation with potassium
permanganate then sediment
If Fe >5 ppm, coatings form filtration.
on leaf surfaces & may reduce 4- chlorination then sediment
photosynthesis. & carbon filtration.
Rock & soil containing
If calcium is present, scale can
gypsum, iron sulfides,
form.
Sulfur other sulfur compounds.
(S) < 33 ppm 33 - 66 > 66 Reverse osmosis.
As part of salinity, can reduce
ppm Industrial wastes,
growth and/or cause plant
sewage, & from coal
injury.
mining operations.
Naturally occurring in Boron leaches quickly from
Needed in very small amounts
groundwater, & from sandy soils, not typically a
by plants.
Boron decaying plant material. problem.
(B) < 1.0 ppm 1.0 – 2.0 > 2.0
When in excess, it is toxic.
ppm Industrial pollutants and Will accumulate in fine textured
from agricultural runoff soils & pose a greater toxicity
Plant sensitivity ranges.
also are sources. threat to sensitive plants.
Dissolved from rock,
< 70 ppm > 200 for soil
salts, & soil.
and water ion
High concentrations can speed
Sodium hazard
Human induced up corrosion by other elements.
(Na+) 70-200 Refer to SAR in this table.
concentrations from Can also burn foliage. Refer to

CU-2014-700
ppm < 70 > 70 for foliar
road salt, fertilizers, SAR in this table.
injury‡
industrial brines, &
reclaimed wastewater.
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Interpreting irrigation water quality reports

Table 1 cotinued. Irrigation water component, its severity range, description of issue, and strategy for managing the problem.

Severity
Component Origin Not a Increasing Severe Issue Management
Problem Problem Problem
From dissolved minerals,
& sea water. < 70 ppm 70 – 300 > 300 for soil
Mobile in the soil.
& water ion Blend or change to an
Chloride
Human induced hazard alternative water source.
(Cl-) Cl can be taken up by roots &
concentrations from
ppm accumulate in leaves causing
road salt, fertilizers, 0 0 - 100∫ > 100 for Reverse osmosis.
toxicity.
industrial wastes and/or foliar injury†
sewage.
High concentrations: succulent
From decaying organic plant growth, tissues not as Fertilization amounts &
material. resource efficient, & plants scheduling should account for
Nitrate
more susceptible to some pests. amount supplied by irrigation
(NO3--N) < 50 50 - 100 > 100
Major contributions from water.
ppm
fertilizers, sewage, & Nitrogen-rich runoff can cause
manure applications. eutrophication in receiving Reverse osmosis.
waters.
The same as total dissolved
Concentration of mineral
solids in clear, non-turbid Refer to:
salts (ex: MgSO4, MgCl,
Total water. Electrical conductivity in this
CaCl, NaHCO3, NaCl,
Dissolved table.
KCl) dissolved in water.
Salts < 500 500 - 2000 > 2000 High salinity- salt accumulation
(TDS) in fine textured soils, hard for Permeability and residual
Refer to electrical
ppm roots to absorb water. sodium chloride in the next
conductivity in this
section.
table.
Determine if sodium dominant.
Indicator of presence
of mineral salts, which Use EC as the initial identifying
Management will be dependent
originate from the that a problem exists.
Electrical on the type and degree of the
earth’s crust.
Conductivity < 0.50 or problem.
0.50 - 0.75 0.75 – 3.0 Further evaluation is needed
(EC) > 3.0
Salts contribud by: to determine if the problem is
mmhos/cm Refer to water permeability in
fertilizers, organic total dissolved salts, sodium,

CU-2014-700
the next section.
matter, & treated and/or HCO3- & CO32-.
wastewater.
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Interpreting irrigation water quality reports

Table 1 cotinued. Irrigation water component, its severity range, description of issue, and strategy for managing the problem.

Severity
Component Origin Not a Increasing Severe Issue Management
Problem Problem Problem
Regulates plant nutrient & soil
Measure of hydrogen ion
elements availability.
(H+) concentration.
Indicates a problem exists,
Logarithmic scale 1-14:
Normal < 6.0 or continue to evaluate.
1 = acidic Inject an acid or base into the
pH range: > 8.0
7 = neutral irrigation water.
6.5 – 8.0 Alkaline water: high in CO3- and
14 = alkaline.
HCO32- and/or salinity.
Water pH fluctuates
pH <5.5 or >8.5 can cause
diurnally & seasonally.
corrosion of pipes & equipment.
> 3.0 for soil
< 1.5 1.5 – 3.0
Dissolution of limestone and water ion
Bicarbonate Deposits (milky spots) form
and dolomite, & from hazard Inject acid into irrigation water
(HCO3-) when reacting with Ca2+ & Mg2+
atmospheric carbon to lower the pH.
meq/L <1.5 1.5 – 8.5 to form insoluble precipitates.
dioxide. > 8.5 for
foliar‡
Carbonate Deposits (milky spots) form
Refer to bicarbonate < 0.5 Inject acid into irrigation water
(CO32-) 0.5 – 1.65 > 1.65 when reacting with Ca2+ & Mg2+
(HCO3-). meq/L to lower the pH.
meq/L to form insoluble precipitates.
Blend or change to an
High sodium hazard: alternative water source.
Sodium
1- sodium is disproportionately
Absorption
abundant. Apply a leaching fraction with
Ration (SAR)
2- soils may disperse reducing every irrigation.
Sodium hazard
porosity
or measured by comparing
3- salt crust may reduce Inject S or Ca2+ into the water.
the concentration <10 meq/L* 10 - 18 > 18
infiltration
Adjusted of sodium to that of
4- harder for roots to absorb Reverse osmosis.
Residual calcium & magnesium.
water.
Sodium
Disrupt soil surface to break
(Adj RNa)
Fine textured soils more any crusts & for aeration.

CU-2014-700
meq/L
affected than sandy soils.
Incorporate deep drainage.
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Interpreting irrigation water quality reports

Table 1 cotinued. Irrigation water component, its severity range, description of issue, and strategy for managing the problem.

Severity
Component Origin Not a Increasing Severe Issue Management
Problem Problem Problem
Bicarbonates and carbonates:
high affinity to form insoluble
precipitates with Mg2+ & Ca2+.
Blend or change to an
alternative water source.
When precipitates form, need
excess divalent (2+) cations
Apply a leaching fraction
available to bind with all CO32- &
with every irrigation.
HCO3- with enough remaining to
Residual Residual sodium
aggregate soil particles.
Sodium carbonate: another Inject S or Ca2+ into the
Carbonate method used to assess <1.25 1.25 – 2.50 > 2.50 water.
If inadequate divalent cations
(RSC) Na+ hazard of irrigation
available & irrigation water
meq/L water sources. Reverse osmosis.
contains Na, the pool of Mg & Ca
is used to satisfy the CO32- & HCO3-
Disrupt soil surface to break
leaving no extra divalent cations
any crusts and for aeration.
to aggregate soil particles. The Na
is left to bind with soil particles,
Improve deep drainage.
leading to soil dispersion, less
aggregation, fewer soil pores, &
decreased water infiltration.
† for turfgrass
‡ for sensitive ornamental plants
* not for clay soils
∫ ornamental plants exhibit a wide range of tolerance

CU-2014-700
Interpreting irrigation water quality reports CU-2014-700

Water Permeability Table 2. Water permeability based off of irrigation

Water permeability, also known as infiltration, can water EC and SAR or Adj RNa.
decrease under certain salinity and Na conditions. Match Water permeability problem
up your reported EC (mmhos/cm) and SAR or adj RNa SAR or Adj RNa Unlikely when Likely when EC
(meq/L) values to Table 2 to determine if a problem EC is more than is less than
may exist. In parts of the South Carolina Midlands and
Piedmont regions, pure water problems exist. This is 0-3 0.7 0.4
when there are few minerals in the water (as measured
by EC). Divalent cations such as Ca2+ and Mg2+ act 3-6 1.2 0.3
as bridges to bind soil particles together forming soil
aggregates. When there are few divalent cations, soil 6-12 1.9 0.5
porosity is low with few aggregates and water infiltration
is difficult (EC = 0.3 dS/m, SAR = 0 - 3 meq/L). Raise 12-20 2.9 1.3
the EC over 0.5 dS/m by injecting the water with Ca or
Mg.
20-40 5.0 2.9

In the South Carolina Coastal Plains, high sodium

concentrations are a more common problem. Sodium, a
monovalent cation (Na+), does not form bridges between
References
soil particles thus limiting soil aggregate formation. It
Duncan, Ronny R., Robert N. Carrow, and Michael T.
is also bulky in size and does not allow water close to
Huck. 2008. Turfgrass and Landscape Irrigation Water
the aggregate. When Na+ dominates irrigation water,
Quality: Assessment and Management. CRC Press. Boca
the water soaks in slowly or not at all because the soil is
Raton.
dispersed (has few aggregates) and porosity is low. When
divalent cations (Ca2+ and Mg2+) dominate irrigation
water, even with the presence of Na+, the soil aggregates,
forming pores, and water infiltrates.

SAR is best used for irrigation waters that are low

in HCO3- and CO32-, at concentrations of <120 and
15 mg/L, respectively. When HCO3- and CO32-
concentrations are higher (such as >120 and 15 mg/L,
respectively), adjusted residual soidum (Adj RNa) is best.

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Interpreting irrigation water quality reports CU-2014-700

Prepared by
Dara M. Park
Assistant Professor, Turfgrass, Soil, and Water Quality Extension Specialist
School of Agricultural, Forest, and Environmental Sciences, Clemson University

Sarah. A. White
Assistant Professor, Turfgrass, Soil, and Water Quality Extension Specialist
School of Agricultural, Forest, and Environmental Sciences, Clemson University

Lambert B. McCarty
Professor, Turfgrass, Soil, and Water Quality Extension Specialist
School of Agricultural, Forest, and Environmental Sciences, Clemson University

Nick Menchyk
Postdoctoral Fellow
School of Agricultural, Forest, and Environmental Sciences, Clemson University

Published by
CLEMSON UNIVERSITY COOPERATIVE EXTENSION SERVICE

Citation
Park, D.M., S.A. White, L.B. McCarty and N.A. Menchyk. 2014. Interpreting irrigation water quality reports.
Clemson University Cooperative Extension. CU-14-700.

The Clemson University Cooperative Extension Service offersits programs to people of all ages, regardless of race, color, gender, religion, national origin, disability, political beliefs,
sexual orientation, martial or family status and is an equal opportunity employer. Clemson University Cooperating with U.S. Department of Agriculture, South Carolina Counties,
Extension Service, Clemson, S.C.Distributed in Furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of May 8 and June 30, 1914.