Discusses what an irrigation audit actually tells you. What do the specific tests mean?

1. 1
GLOSSARY OF WATER
So much has been written (or not as the case may be) on water quality and its relation to turf and
soil that there is now a huge amount of confusion occurring within the turf industry. The majority of
work that has been done is in horticulture or broad acre agriculture and this has then been simply
transplanted and applied to the turf industry and sadly the principles used have often been
misrepresented in the marketplace.
Having water of any sort is better than having none at all. Obviously, the quality of water is
important but measures can be taken to improve this to make it more acceptable to use. What these
are will depend entirely on its initial quality.
Applying principles based on horticultural research to for example the irrigation of golf greens with
water of varying quality is fraught with issues. Golf greens possess unique biological and vegetative
characteristics that make such principles questionable if applied exactly. Sand based golf greens as
their name suggests contain a high percentage of sand which means that they are going to behave
differently when irrigated compared to for example a heavier fairway containing a high percentage
of clay. In the case of the latter this can be further extrapolated to take into account the exact type
of clay present as this has an impact on how the fairways behave.
The principle of sodium adsorption ratio (SAR) or SARadj with an upper acceptable limit being
regarded as gospel is also questionable. Golf greens as mentioned earlier are often composed of a
high percentage of sand and in that case a limit of 10 can be regarded as being acceptable. How
often has this figure been used as an acceptable limit rather than the usual figure of 6 (which is
accepted as being the limit in agricultural situations on heavier soils)?
The reason for writing this is to offer a guide for what limits are acceptable and to also explain how
calculations are made. Taking SARadj as a case in point there are a actually a number of means of
calculating this and the most common one used is based on the work by Ayers and Westcott in 1976
which tends to give a slightly inflated value. A much better methology is one based on work by
Suarez in 1981. I’ll discuss this in more detail later.
I have written this as an overview of the testing methologies used. Accompanying this is an easy to
use water quality calculator. All you have to do is enter your test results and it does the rest for you
References are available if required for those of you who feel a need for further reading.

2. 2
Aggressiveness Index. The Aggressive Index (AI) was developed as a measure of how corrosive the
use of irrigation water is on piping. Originally developed to establish the quality of the water that can
be transported through asbestos cement pipe, but can also used to determine if calcium is likely to
be deposited in the form of scale or alternatively “stripped” and thus removed from a soil.
There are two methods for calculating this. The first is by using the pH, calcium hardness in mg/l as
CaCO, and the total alkalinity in mg/l as CaCO by the formula:
Al = pHactual + C + D
Value C is obtained from Table xxx in the appendix by reading the value corresponding to the
calcium hardness (in mg/L CaCO3) of the sample. Value D is obtained from the appendix by reading
the measured value for total alkalinity (in mg/L CaCO3) of the sample using the same table.
The second method uses the same inputs but is actually easier to calculate the end result as it is
determined by:
AI= pHactual + LOG (hardness ppm * alkalinity ppm)
Both of these methods do not take into account temperature and so are not as accurate as another
measure called the Langellier Saturation Index discussed later.
Aggressive index values less than 10.0 indicate highly aggressive water, values between 10.0 and
12.0 indicate moderately aggressive water, and values greater than 12.0 indicate nonaggressive
waters.
Alkalinity
This is the amount of carbonate and bicarbonate expressed as ppm CaCO3. Alkalinity is a measure of
a water's acid neutralizing capacity and is primarily a function of carbonate, bicarbonate and
hydroxide content. Excessive alkalinity levels may cause scale formation. Alkalinity is the main
control factor for the aggressiveness of the water. Aggressive water will have a tendency to react
with metal pipes and corrode them. Incrusting water will have a tendency to clog pipes with salt and
reduce their through flow over time.
Anions
These are negatively charged ions and in the interpretation of water analysis include: chloride (Cl -
),
sulphate (SO4
--
), carbonate (CO3
--
), bicarbonate (HCO3
-
), and nitrate (NO3
--
).
In some reports elemental sulphur (S) and nitrogen (N) are reported rather than sulphate (SO4
--
) or
nitrate (NO 3
—
respectively). If this is the case:
To convert S to SO4
-
multiply S by 2.996. If you wish to covert SO4
-
to S then multiply the SO4
-
figure
by 0.334.
To convert N to NO3
-
multiply N by 4.429. If you wish to covert NO3
-
to N then multiply the NO3
-
figure by 0.226.

3. 3
Bicarbonate (HCO3)
Bicarbonate is the major form of alkalinity. High levels of bicarbonate in water can increase the
concentration of sodium in water, raise soil pH, and have a negative impact on soil permeability.
Cations
These are positively charged ions. Other positive cations include: sodium (Na+), potassium (K+) ,
magnesium (Mg2+) , calcium (Ca2+) , Iron (Fe2+), and manganese (Mn2+).
Calcium and magnesium.
These minerals exist as positively charged ions (cations) in water, and they counteract the damaging
effects of sodium. Their concentrations are used in the calculation of SAR. Small concentrations of
calcium carbonate combat corrosion of metal pipes by laying down a protective coating. Calcium
contributes to the total hardness of water.
Calcium Carbonate Precipitation Potential (CCPP)
This provides a quantitative measure of the calcium carbonate deficit or excess of the water, giving a
more accurate guide as to the likely extent of CaCO3 precipitation. The CCPP is a means of
calculating the quantity of calcium carbonate that can be precipitated from saturated waters or
dissolved into unsaturated waters.
A measure of the corrosivity of water for different values of CCPP is presented in the table below.
Corrosivity State of water CCPP Value, mg/L CaCO3
Scaling (protective) >0
Passive 0 to -5
Mildly corrosive -5 to -10
Corrosive (aggressive) < -10
Carbonate (CO3)
Carbonate can only exist if the pH of the water exceeds 8.3. Carbonate and bicarbonate ions in the
water combine with calcium and magnesium to form compounds which precipitate out of solution.
This increases the concentration of sodium as removing calcium and magnesium increases the
sodium hazard to the soil from irrigation water. The increased sodium hazard is often expressed as
"adjusted SAR." The increase of "adjusted SAR" over the SAR is a relative indication of the increase in
sodium hazard due to the presence of these ions.
Chloride.
Although an essential nutrient to growth, toxic levels of it in water can restrict plant growth. Water
chloride concentrations up to 70 ppm are safe for all plants. From 70 to 140 ppm chloride, sensitive
plants may incur some injury. From 140 to 350 ppm chloride moderately tolerant plants will likely
incur injury. Severe problems can be expected at concentrations above 350 ppm chloride. Chloride
contributes to the overall water salinity, and when concentrations are high enough, can be toxic to
plants. Turfgrasses are not particularly sensitive to chloride, and can tolerate levels up to 100 mg/L.
Turfgrasses can sustain injury when irrigated with water containing >355 mg/L of chloride.

4. 4
EC.
EC is a measure of the degree in which water conducts electricity. It is determined by passing an
electrical current through a water sample and recording the resistance in mmhos/cm or dS/m. EC is
used to estimate the concentration of Total Dissolved Solids (TDS) in water, using the following
equation:
TDS (ppm or mg/L) = EC (mmhos/cm or dS/m) × 640
Hardness.
Hardness is the term for the calcium or magnesium carbonate dissolved in water as Ca++, Mg++, and
HCO3- (bicarbonate) ions. There are two measures of water hardness, hardness and alkalinity.
Hardness measures the amount of positive calcium and magnesium ions; alkalinity the negative
bicarbonate ions. Both measures are usually given in calcium carbonate, i.e. scale, equivalent units
(abbreviated as CaCO3). This means when one unit of scale precipitates out of the water, hardness
and alkalinity measured in CaCO3 units go down by one unit each.
Alkalinity and hardness levels need not be the same, since the bicarbonates can be associated with
potassium or sodium, and the calcium or magnesium with chlorides or sulphates. Usually, alkalinity
is less than hardness, although some mineral waters and ion exchange softened waters rich in
sodium or potassium may have higher levels of alkalinity.
Iron (Fe)
At levels above 0.3 mg/L, iron can cause staining of for example fencing around ovals. The
precipitation of excessive iron causes a reddish brown colour in the water. It may also promote the
growth of iron bacteria, leaving a slimy coating in piping. The presence of iron bacteria can also
cause a rotten egg' odour in the water and sheen on the surface of the water.
Langelier Saturation Index
The Langelier Saturation Index (sometimes Langelier Stability Index) is a calculated number used to
predict the calcium carbonate stability of water. To put this another way it is a measure of a
solution’s ability to dissolve or deposit calcium carbonate and predicts whether a water will dissolve,
precipitate or is in equilibrium with calcium carbonate.
The LSI is expressed as the difference between the actual system pH and the saturation pH and is
calculated thus:
LSI = pH (measured) - pHs
If the actual pH of the water is below the calculated saturation pH, the LSI is negative and the water
has a very limited scaling potential. If the actual pH exceeds pHs, the LSI is positive, and being
supersaturated with CaCO3, the water has a tendency to form scale. At increasing positive index
values, the scaling potential increases. The Saturation Index is typically either negative or positive
and rarely 0. A Saturation Index of zero indicates that the water is “balanced” and is less likely not to
cause scale formation.
If LSI is negative: No potential to scale, the water will dissolve CaCO3
If LSI is positive: Scale can form and CaCO3 precipitation may occur

5. 5
If LSI is close to zero: Borderline scale potential. Water quality or changes in temperature, or
evaporation could change the index.
In practice, water with an LSI between -0.5 and +0.5 will not display enhanced mineral dissolving or
scale forming properties. Water with an LSI below -0.5 tends to exhibit noticeably increased
dissolving abilities while water with an LSI above +0.5 tends to exhibit noticeably increased scale
forming properties.
It is also worth noting that the LSI is temperature sensitive and this seems to be seldom taken into
consideration when water testing is carried out and means that the water can behave slightly
differently depending on the time of year.
The LSI becomes more positive as the water temperature increases. This has particular implications
in situations where tank water is used.
In order to calculate the LSI, it is necessary to know the alkalinity (mg/l as CaCO3), the calcium
hardness (mg/l Ca2+
as CaCO3), the total dissolved solids (mg/l TDS), the actual pH, and the
temperature of the water (o
C). If TDS is unknown, but conductivity is, one can estimate mg/L TDS
using a table.
Where:
pH is the measured water pH
pHs is the pH at saturation in calcite or calcium carbonate and is defined as:
pHs = (9.3 + A + B) - (C + D)
Where:
A = (Log10 [TDS] - 1) / 10
B = -13.12 x Log10 (o
C + 273) + 34.55
C = Log10 [Ca2+
as CaCO3] - 0.4
D = Log10 [alkalinity as CaCO3]
Corrosive characteristics Langellier Index Aggressive Index
Highly aggressive <-2.0 <10.0
Moderately aggressive -2.0 to 0.0 10.0 to 12.0
Nonaggressive >0.0 >12.0

6. 6
Larsen Skold Index
Another index is Larson index (LI) which describes the corrosivity of water towards mild steel. Larson
considered chlorides, sulphates and total alkalinity and is the ratio of equivalents per million (epm)
of sulphate (SO4 --) and chloride (Cl- ) to the epm of alkalinity in the form of bicarbonate plus
carbonate.
• Larson-Skold Index <0.8 Chlorides and sulphates will probably not interfere with natural film
formation.
• Larson-Skold Index 0.8 – 1.2 Chlorides and sulphates will probably interfere with natural film
formation and higher corrosion rates can be anticipated.
• Larson-Skold Index >1.2; High corrosion rates can be expected and in the case of scale this is
unlikely to form.
Millequivalent (MEQ) Mg/l (ppm) values may be converted to milliequivalents /l by multiplying the
milligrams per litre (ppm) by the multiplication factors given below.
Start with concentration, divide by mole wt., multiply by charge:
XX mg/L / Molecular weight x Charge = MEQ
Example: NaCl in solution, Na = 109 mg/L (109 ppm): 109/23*1 = 4.73 MEQ
Cl = 177 mg/L (177 ppm): 177/35.5*-1 = -4.98 MEQ
Always remember that if the total cation and anion MEQ’s are not balanced, some error exists in the
analysis.
Ca Cl CO 3 Fe HCO 3 K Mg Mn NO 3 Na P SO4
Molecular weight 40 35.5 60 56 61 39 24 55 124 23 31.7 96
Valence 2 1 2 3 1 1 2 2 2 1 1 2
Equivalent weight 20 35.5 30 18.7 61 39 12 27.
5
62 23 31.7 48
Multiply ppm by
this number to
give Meq
2.5 1.41 1.67 0.82 1.28 4.1 0.81 2.18 1.04
Nitrate
Nitrate in irrigation water is plant available and should be taken into consideration with any
nutritional programme. At high concentrations, this can supplement the nitrogen applied in a regular
fertilization program. At concentrations greater than 30 ppm NO3-N, toxicity problems can be
expected.

7. 7
pH
pH is a measure of how acidic/basic water is. The range goes from 0 - 14, with 7 being neutral. With
a pH of less than 7 this means the water is acidic, whereas with a pH of greater than 7 this indicates
it is alkaline (also known as a base). pH is really a measure of the relative amount of free hydrogen
and hydroxyl ions in the water. Water that has more free hydrogen ions is acidic, whereas water that
has more free hydroxyl ions is basic. Since pH can be affected by chemicals in the water, pH is an
important indicator of water that is changing chemically. pH is reported in "logarithmic units," like
the Richter scale used for measuring the size of earthquakes. Each number represents a 10-fold
change in the acidity/basicness of the water. Water with a pH of 5 is ten times more acidic than
water having a pH of six.
pHc
The tendency of water to cause calcium precipitation can be predicted although there is actually no
proven practical method to evaluate how serious the problem will be since it depends upon many
factors. You can only give a measure of how serious the potential problem is. A first approximation
of the calcium precipitation can be made using the saturation index which simply says that upon
reaching the calcium saturation point in the presence of bicarbonate, lime (CaCO3) will precipitate
from the solution. The saturation index is defined as the actual pH of the water (pH) minus the
theoretical pH (pHc) that the water could have if in equilibrium with CaCO3.
Saturation Index = pH - pHc
Positive values of the index (pH > pHc) indicate a tendency for CaCO3 to precipitate from the water
whereas negative values indicate that the water will dissolve CaCO3.
pHs
Whether and how much scale precipitates depends on the water's alkalinity, hardness, temperature,
and total dissolved solids. These factors together define a quantity called pH at saturation, or pHs.
pHs indicates the pH level at which the measured calcium/magnesium bicarbonate level is at
equilibrium saturation. If the pHs exceeds the water's actual pH, no scale will form, in fact, existing
scales will tend to dissolve into the water. The water will tend to strip for example calcium from the
soil. If the pHs is less than the actual pH, lime will precipitate out of the water until the pH balance is
restored. This water will tend to deposit for example calcium.
The formula for pHs is as follows: The logs are base 10, T is temperature in centigrade, S is mg/l total
dissolved solids, H is mg/l hardness, and A is mg/l alkalinity, both stated in CaCO3 equivalent units.
pHs = 44.15 + log(S)/10 - 13.12*log(T + 273) - log(H) - log(A)
As discussed earlier the quantity pH - pHs is called the Langelier Index or LI (sometimes
called the Saturation Index or SI). The LI formula is:
LI = pH + 13.12*log(T + 273) + log(H) + log(A) - log(S)/10 - 44.15
Potassium
Potassium behaves much like sodium, but it is usually found in only small amounts in water.

8. 8
Residual Sodium Carbonate (RSC)
The sodium permeability hazard for irrigation water is usually assessed when bicarbonate and
carbonate levels are >120 and 15 mg/L, respectively. Residual sodium carbonate (RSC) is a common
means of assessing the sodium permeability hazard, and takes into account the
bicarbonate/carbonate “and” calcium/magnesium concentrations in irrigation water. RSC is
important because it is not the absolute bicarbonate and carbonate concentrations that are
important, but instead, the relative concentrations of bicarbonate and carbonate compared to
concentrations of calcium, magnesium, and sodium.
RSC is calculated as follows:
RSC (meq/L) = (HCO3
-
+ CO3
-2
) - (Ca + Mg)
Note that for this equation, all concentrations are expressed in meq/L (see earlier). Typically, water
with a RSC value of 1.25 meq/L or lower is safe for irrigating turf. RSC values between 1.25 and 2.5
meq/L is marginal, and above 2.5 meq/L is considered excessive.
Ryznar Stability Index.
This helps you determine the scaling potential of water. It can be calculated from the following
equation:
RSI = 2 (pHs) - pH
Where:
• pH is the measured pH of the water and;
• pHs is the pH at saturation in calcite or calcium carbonate.
 RSI is 6 or lower then the water has a tendency to scale and precipitate calcium carbonate.
• RSI is 7 then calcium bicarbonate formation does not produce a protective corrosion inhibiting
film.
• RSI is 8 or higher, corrosion of steel (and zinc) becomes an increasing problem and the water has a
tendency to dissolve calcium carbonate CaCO3.
RI Indication (Ryznar 1942)
RI<5,5 Heavy scale will form
5,5 < RI < 6,2 Scale will form
6,2 < RI < 6,8 No difficulties
6,8 < RI < 8,5 Water is aggressive
RI > 8,5 Water is very aggressive
RI Indication (Carrier 1965)
4,0 - 5,0 Heavy scale
5,0 - 6,0 Light scale
6,0 - 7,0 Little scale or corrosion
7,0 - 7,5 Corrosion significant
7,5 - 9,0 Heavy corrosion
>9,0 Corrosion intolerable
Ryznar gives only an indication about the aggressiveness of the water but Carrier gives an indication
about the scale and corrosion potential of the water.

9. 9
Salinity
Saline irrigation water contains dissolved substances known as salts. The majority of the salts
present in irrigation water are chlorides, sulphates, carbonates, and bicarbonates of calcium
magnesium, sodium, and potassium. While salinity can improve soil structure, it can also negatively
affect turf growth.
Soil water salinity can affect soil physical properties by causing fine particles to bind together into
aggregates. This process is known as flocculation and is beneficial in terms of soil aeration, root
penetration, and root growth. Although increasing soil solution salinity has a positive effect on soil
aggregation and stabilization, at high levels salinity can have negative and potentially lethal effects
on the turf itself. As a result, salinity cannot be increased to maintain soil structure without
considering potential impacts on plant health.
SAR
The sodium adsorption ratio (SAR) expresses the sodium hazard of water, and is calculated from
sodium, calcium and magnesium concentrations in water. Calcium and magnesium are the good
guys and counter sodium’s effect on soil. The SAR of a water sample is the proportion of sodium
relative to calcium and magnesium. Since it is a ratio, the SAR has no units.
Sodium in irrigation water can accumulate in soil and result in undesirable physical soil
characteristics. This can be seen in the behaviour of the soil under varying moisture contents. When
wet, soil with high sodium levels has reduced water permeability and when dry it becomes very
hard. Sodium can also accumulate in soil to sufficiently large amounts such that plant uptake of
sodium becomes toxic to the plant. This means sodium has a double wammy effect. It can effect soil
structure and also affect the turf directly.
Fine textured soils under low leaching conditions are most susceptible to degradation from irrigating
with water that has moderate SAR values (3 to 6). From the perspective of inducing soil permeability
problems, SAR and electrical conductivity both need to be considered. Low salinity water
(‘light’water) is usually low in calcium and magnesium and consequently it increases the deleterious
effect of sodium in water. Calcium and magnesium play a major role in maintaining structure of clay-
containing soils. If water with excess sodium and low calcium and magnesium is applied frequently
to clay soils, the sodium will tend to displace calcium and magnesium on clay particles, resulting in
breakdown of structure, precipitation of organic matter, and reduced permeability.
SAR is used to assess the relative concentrations of sodium, calcium, and magnesium in irrigation
water and provide a useful indicator of its potential damaging effects on soil structure and
permeability.
Typically a SAR value below 3.0 is considered very safe for turfgrasses. Over time, water with a SAR
of 9.0 or above can cause significant structural damage to clay soils. Sandy soils are not as
susceptible to structure and permeability problems, and can tolerate higher SAR values (up to 10
in most cases).

10. 10
EC dS/m EC dS/m EC dS/m
SAR No Problem Slight to moderate Severe problem
0 to 3 > 0.9 0.9 to 0.2 < 0.2
3 to 6 > 1.3 1.3 to 0.25 < 0.25
6 to 12 >2.0 2.0 to 0.35 < 0.35
12 to 20 > 3.1 3.1 to 0.9 < 0.9
20+ > 5.6 5.6 to 1.8 < 1.8
Guidelines for saline-sodic water quality suitable for irrigation, presented in terms of reduced
infiltration (After Ayers and Tanji, 1981).
Sodicity
Sodicity refers specifically to the amount of sodium present in irrigation water. Irrigating with water
that has excess amounts of sodium can adversely impact soil structure, making plant growth
difficult.
Sodium has the opposite effect of salinity on soils. The primary physical processes associated with
high sodium concentrations are soil dispersion and clay platelet and aggregate swelling. The forces
that bind clay particles together are disrupted when too many large sodium ions come between
them. When this separation occurs, the clay particles expand, causing swelling and soil dispersion.
This soil dispersion results in clay particles plugging soil pores, resulting in reduced soil permeability.
When soil is repeatedly wetted and dried and clay dispersion occurs, it then reforms and solidifies
into almost cement-like soil with little or no structure. The three main problems caused by sodium-
induced dispersion are reduced infiltration, reduced hydraulic conductivity, and surface crusting.
Calcium and magnesium will generally keep soil flocculated because they compete for the same
spaces as sodium to bind to clay particles. Increased amounts of calcium and magnesium can
reduce the amount of sodium-induced dispersion.
Sodium
Sodium exists in nearly all irrigation water and is not necessarily a cause for concern unless high
concentrations are present. High concentrations (> 70 mg/L) can be detrimental to both turf and
soils. Sodium in irrigation water can be absorbed by roots and foliage, and foliar burning can occur if
sufficient amounts accumulate in leaf tissue. Grasses grown on golf course putting greens (creeping
bentgrass and annual bluegrass) are particularly susceptible to sodium toxicity because they are
mowed very short and irrigated frequently often during the heat of the day.
Sulphate
Sulphate exists in water as a negatively charged ion. It contributes to the total salt content.
Temperature
Whether and how much scale precipitates depends on the water's alkalinity, hardness, temperature,
and total dissolved solids. These factors together define a quantity called pH at saturation, or pHs
(discussed earlier).
Total dissolved solids
Total dissolved solids (effectively dissolved salts) is a measure of salinity and is a measure of total
salts in solution in ppm or mg/L. Water salinity is derived primarily from the ions of calcium,

11. 11
magnesium, sodium, chloride and bicarbonates. Saline water induces a physiological drought in
plants. Furthermore, salts applied in irrigation water are left behind in the soil following
evapotranspiration, which leads to soil degradation. If saline water is to be used, it should be
generously applied in order to leach salts and prevent salt accumulation. TDS is occasionally referred
to as total dissolved salts (also abbreviated TDS) or total soluble salts (TSS), and both are determined
using the same equation.
Acceptable TDS concentrations for turfgrass irrigation range from 200 to 500 mg/L (EC = 0.31 to 0.78
mmhos/cm). TDS concentrations higher than 2,000 mg/L (EC = 3.1 mmhos/cm) can damage
turfgrasses. If using irrigation water with a TDS concentration higher than 500 mg/L, attention
should focus on irrigation duration and frequency, drainage, and turfgrass species selection.