Environmental Health
Queensland Health Forensic & Scientific
Services
The following explanatory notes provide a summary overview of key aspects of individual parameters in a standard chemical water analysis. For ease of reference, the layout of these guidance notes matches the standard chemical report from Queensland Health Forensic and Scientific Services (QHFSS).
There are two (2) different guideline values for drinking water quality parameters under the NHMRC
Australian Drinking Water Guidelines (ADWG) – these are “health” related and “aesthetic”.
A health related guideline value is the concentration or measure of a water quality characteristic that, based on present knowledge, does not result in any significant risk to the health of the consumer over a lifetime of consumption.
Health related guideline values are derived from the acceptable daily intake (ADI) and set at about 10% of the ADI for an adult weight of 70kg for a daily water consumption of 2 litres. The health values are very conservative, include a range of safety factors and always err on the side of safety.
An aesthetic guideline value is the concentration or measure of a water quality characteristic that is associated with acceptability of water to the consumer, e.g. appearance, taste and odour.
For more detail information on individual parameters consult the ADWG.
Unit abbreviations are included in Table 2 at the end of these Guidance Notes.
There is no ADWG value for conductivity. Conductivity is related to the concentrations of ions capable of carrying an electrical current. It is an estimation of the total dissolved solids or salinity in water. Levels up to 800

S/cm are acceptable in drinking water.
Rain water has a conductivity of between 10
(>50,000

S/cm).

S/cm and 20

S/cm whilst sea water is around 50,000

S/cm.
The conductivity of bore waters can vary widely from good quality (<200

S/cm) to very saline
The units for pH is the “Standard pH unit” (Std pH Units) and there is no health related guideline value for pH. However, for aesthetic reasons the range should be within pH 6.5 to pH 8.5.
While extreme pH values (<4 and >11) may adversely affect health, there are insufficient data to set a health guideline value. It should be noted that rainwater is always acidic (pH varies between about pH 4.5 to pH
6.5) since moisture (H
2
O) in the air absorbs carbon dioxide (CO
2
) producing carbonic acid (H
2
CO
3
). The best way to neutralise the acidity in the water is to suspend a bag of limestone (or marble – calcium carbonate
CaCO
3
) in the centre of the rainwater tank or simply add lime - calcium hydroxide Ca(OH)
2
. Concrete rainwater tanks will neutralise the acidity in rainwater naturally because concrete is essentially alkaline.
Some pH characteristics are as follows:

<pH 6.5 may be corrosive
Page: 1 of 8
Document Number: 28162T1
Approver/s: Henry OLSZOWY

Interpretation of Water Results – Standard Water Analyses
 pH 8 progressively decreases efficiency of chlorination

>8.5 may cause scale and taste problems
Hardness in water is caused by the presence of high levels of calcium (Ca
++
) and magnesium (Mg
++
) ions. These ions combine with carbonate (CO
3
2 ⎯
) dissolved in water to produce scale which is composed of insoluble carbonates (CaCO3 and MgCO3). The scale builds up on plumbing parts, eventually causing blockages to water flow. There is no health related guideline value for total hardness. To minimise undesirable build-up of scale in hot water systems total hardness in drinking water should not exceed 200mg/L as calcium carbonate (CaCO
3
). Recommendations for hardness are as follows:

<150 (mg CaCO
3

/L) acceptable
200 (mg CaCO
3
/L) aesthetic guideline NHMRC

>150 <350 (mg CaCO
3
/L) softening is recommended for laundry dilutions

>350 (mg CaCO
3
/L) softening is considered necessary for laundry and ablutions
Temporary hardness is the portion of the total hardness which is due to calcium and magnesium bicarbonates – Ca(HCO
3
)
2
and Mg(HCO
3
)
2
. This hardness is termed “temporary” because it is assumed that eventually the insoluble carbonates are formed thereby removing this part of the total hardness from the water. Temporary hardness can be removed by boiling the water. The bicarbonates form the carbonates as protective scale.
Boiling: Ca(HCO
3
)
2

CaCO
3
+ CO
2
+ H
2
O
The theoretical amount of temporary hardness which may form is governed by the availability of Ca
++
and
Mg
++
on one side and bicarbonate on the other side i.e. the smaller equivalent concentration of the two would decide the level of temporary hardness present.
Temporary Hardness = Lesser of Alkalinity (as mg CaCO
3
/L) or Total Hardness (as mg CaCO
3
/L)
Example:
Alkalinity = 500 (mg CaCO
3
/L)
Total Hardness = 550 (mg CaCO
3
/L)
Thus the lesser of the two is the alkalinity, therefore:
Temporary Hardness (mg CaCO
3
/L) = 500 (mg CaCO
3
/L)
There is no ADWG value for Temporary Hardness.
Alkalinity is due to bicarbonate (HCO
3
¯), carbonate (CO
3
2
¯) and hydroxyl (OH¯) anions and is a measure of the water’s resistance (or buffering effect) to pH change when acid is added. It is expressed as the sum of all the acid titrateable bases. The alkalinity is reported as mg CaCO
3
/L. Other bases, besides
HCO
3
¯, CO
3
2
¯ and OH¯ ions, may be present e.g. borates, phosphates, silicates etc. There is no NHMRC guideline value for alkalinity but it does contribute to the amount of total dissolved solids (TDS) which has an aesthetic guideline value of 500mg/L. Levels between 30 to 400mg/L are suitable for drinking water.
: Residual Alkalinity (RA) is defined as the remainder of carbonate and bicarbonate after subtracting the equivalent of Ca
++
and Mg
++
i.e. if the equivalent concentrations of HCO
3
¯ and CO
3
2
¯ ions exceed the concentrations of Ca
++
and Mg
++
, the water is said to contain residual alkalinity.
RA is expressed as milli-equivalents per litre.
Residual alkalinity serves as a commonly used index to determine the suitability of the water for irrigation purposes. It is calculated by subtracting the concentrations of calcium and magnesium from the concentrations of carbonate and bicarbonate expressed in milli-equivalents per litre (meq/L).
RA = meq(HCO
3
¯ + CO
3
2
¯) – meq(Ca
2+
+ Mg
2+
)
Page: 2 of 8
Document Number: 28162T1
Approver/s: Henry OLSZOWY

Interpretation of Water Results – Standard Water Analyses
Example:
Ca
2+
= 7.21mg/L = 0.36meq/L weight of Ca
++
is 20.04)
(to calculate meq/L, divide mg/L by the equivalent weight. In this case, the equivalent
Mg
2+
= 3.09mg/L = 0.254meq/L (Equiv Wt Mg
++
= 12.156)
HCO
3
¯ =
CO
3
2
¯ =
RA =
=
64.98mg/L = 1.065meq/L (Equiv Wt HCO
0.059mg/L = 0.002meq/L (Equiv Wt of CO meq(HCO
3
¯ + CO
3
2
¯) – meq(Ca
2+
(1.065 + 0.002) – (0.36 + 0.254)
+ Mg
2+
)
3
¯ - 61.02)
3
2
¯ = 30)
= 0.453meq/L
A high RA will be damaging to soil structure and crop growth because Ca and Mg will be precipitated from soil solutions increasing the relative concentration of Na (see Table 1 below). There is no ADWG value for
Residual Alkalinity.
: The SAR is a parameter relevant to irrigation use and is a measure of the ratio of sodium to calcium and magnesium. When the ratio of sodium to calcium and magnesium is high, there is an adverse effect on soil structure and permeability, which can reduce crop yields and growth rates. Generally, the higher the SAR value, the more unsuitable is the water for low salttolerant crops (see Table 1). SAR is calculated as follows:
SAR = meqNa
+
/
 meq(Ca
++
+ Mg
++
)/2
Example:
Na
+
= 16.1mg/L = 0.7meq/L; Ca
++
= 7.21mg/L = 0.36meq/L; Mg
++
= 3.09 = 0.254 meq/L
SAR = 0.7/

=
(0.36 + 0.254)/2
0.7/

0.2047
In this case, there is no sodium problem and the water is regarded as good quality, suitable for a wide range of crops.
There is no ADWG guideline value for SAR. Table1 below shows a range of SAR and RA values together with their significance.
Table 1: Range of SAR and RA values and their significance.
Sodium Absorption Residual
Ratio (SAR)
<3
3 to 6
Alkalinity
(meq/L)
<1.25
<1.25
6 to 8
<6
8 – 14
<14
<14
<1.25
1.25 – 2.5
<2.5
2.5 – 5.0
>5
Comme nts
No Na Problems
Low Na, few problems except with Na sensitive crops (e.g. pecan nut, avocado, papaw, strawberry)
Medium sodium, increasing problems, use gypsum and non-sodium sensitive crops
Medium sodium, increasing problems, use gypsum and non-sodium sensitive crops
High sodium, not generally recommended
High sodium, not generally recommended
Very high Na, unsuitable
2
There is no ADWG value for silica. The total silica content of water is composed of
“Reactive Silica” and “Unreactive Silica”. Reactive silica, though it has anionic characteristics, is not counted as an anion in terms of balancing a water analysis but it is counted as a part of total dissolved solids
Page: 3 of 8
Document Number: 28162T1
Approver/s: Henry OLSZOWY

Interpretation of Water Results – Standard Water Analyses
(TDS). Unreactive silica is polymerized or colloidal silica, acting more like a solid than a dissolved ion.
Total dissolved ions is the summation of the total dissolved cations and total dissolved anions.
Total Dissolved Ions (TDI) = Total cations (mg/L) + Total anions (mg/L)
TDI is related to the total ionic strength (

) of the water where all parameters are expressed in milliequivalents/L except for CO
3
2 ⎯ and HCO
3
⎯ (mg/L) in the equation below:

= [Na + K + Cl + F + NO
3
+ 2(Ca + Mg + SO
4
) + CO
3
/15.0025 + HCO
3
/61.02]/2000 + (H +OH)/2
There is no ADWG value for total dissolved ions.
The total dissolved solids include silica plus cations plus anions but exclude bicarbonate because bicarbonate is lost when the dissolved material is dried. TDS is calculated as follows:
TDS = SiO2 (mg/L) + Cations (mg/L) + Anions (mg/L) – (0.5083 x HCO
3
⎯
)
There is an empirical relationship between TDS and the Conductivity known as the I/C ratio. The “I” represents total dissolved solids minus silica in mg/L (I = TDS mg/L – Silica mg/L) and “C” is the conductivity in

S/cm.
I/C is calculated as follows and generally ranges in value from about 0.4 to 0.7 (average usually 0.5):
I
C
= (TDS – Silica) mg/L
Cond (

S/cm)
≈
0.5
There is no health related guideline value for total dissolved solids. However, for aesthetic reasons (taste) the concentration of total dissolved solids in drinking water should not exceed 500 mg/L. Up to 1000mg/L may be acceptable depending on taste.
: The unit for colour is that produced by 1 mg/L of platinum in the form of the chloroplatinate ion in the presence of 2 mg/L of cobalt(II) chloride hexahydrate. Colour measurement is expressed in Hazen units (HU) which is interpreted as mg of Pt/Co Colour/L (PCU).
The term true colour refers to the colour of water from which the turbidity has been removed by filtration through a 0.45
 m filter. Apparent colour is the colour produced both by dissolved substances and by suspended matter in the water where the turbidity has not been removed.
There is no health related guideline value for true colour. However, for aesthetic reasons values should be
<15HU. Up to 25 HU is acceptable if turbidity is low. If there is high colour at the time of disinfection, then the water should be checked for disinfection by products such as trihalomethanes.
Turbidity occurs as a result of a suspension of fine colloidal particles that do not readily settle out of solution and can result in “cloudiness”. Turbidity is expressed in Nephelometric Turbidity Units (NTU) and is determined by an instrument known as a Nepholometer. Turbidity causes light to be scattered and absorbed rather than transmitted in straight lines through a sample and the Nepholometer measures the relative amount of light able to pass through the solution.
There is no health related guideline value for turbidity. However, for aesthetic reasons turbidity values should be <5 NTU. Waters with a turbidity <1 NTU can be safely disinfected without cause for concern for micro-organisms being protected by small particles. However, it is possible that waters with a turbidity >1
NTU may shield some micro-organisms from disinfection.
Page: 4 of 8
Document Number: 28162T1
Approver/s: Henry OLSZOWY

Interpretation of Water Results – Standard Water Analyses
sat
The pHs is a calculated parameter which represents the theoretical pH value which the water would attain if it were to be saturated with CaCO
3
. The pHs calculation is very complex and beyond the scope of these notes. The significance of pHs is that it is used to calculate the
Langelier Saturation Index (see below). There is no ADWG value for pHs.
The
Langelier Saturation Index (LSI) is an approximate measure of the degree of saturation of water with calcium carbonate. If the LSI is <0, the water is under-saturated with respect to CaCO
3
and therefore the water cannot form a protective coating of scale on plumbing parts. The LSI depends on 4 factors:
1.
pH
2.
Calcium concentration
3.
Alkalinity
4.
Temperature
The LSI is calculated as follows:
LSI = pH – pHs
Significance of LSI:

LSI <0: Water is under-saturated with respect to CaCO
3 and cannot form a protective scale layer. For SI values in the range -8 to -5, the water will be generally quite acidic (no alkalinity) and will be corrosive. The corrosivity can be controlled by addition of lime (Ca(OH)
2
)or soda ash (Na
2
CO
3
).
 LSI = 0: Water is just saturated with CaCO
3
. This is an ideal situation whereby a protective scale coating will form slowly provided the water is not high in hardness.

LSI = 0 to 1: Water is saturated with CaCO
3 and will produce a protective scale coating on pipes.
 LSI >1: The water has a high ability to form scale and capable of clogging up pipes.
Example: pH = 7.2, pHs = 8.9
Saturation Index = 7.21 – 8.86
In this case, the water is under-saturated with respect to CaCO
3
and would not form a protective scale layer.
There is no ADWG value for saturation index.
The Mole Ratio is an index of corrosion. High values indicate high corrosive powers. If mole ratio >2, the water has high corrosivity. Mole Ratio is calculated as follows:
Mole Ratio = log (1.692 [Cl ⎯ ]/[CO
3
2 ⎯ ])
Example:
[Cl ⎯ ] = 8.5mg/L; [CO
3
2 ⎯ ] = 0.059
Mole Ratio = log (1.692 x 8.5/0.059)
There is no ADWG value for Mole Ratio.
: The FM provides another indication for the suitability of the water for irrigation use. It is the ratio of the sum of Mg
++
and Ca
++
divided by Na
+
expressed as meq/L. When comparing the formulae for FM and SAR, it can be seen that one is almost the reverse of the other. In this case however, the higher the FM value, the more suitable is the water for irrigation. FM is calculated as
Page: 5 of 8
Document Number: 28162T1
Approver/s: Henry OLSZOWY

Interpretation of Water Results – Standard Water Analyses follows:
FM = meq/L
++
+ Mg
++
)/meqNa
+
Example
Na
+
= 16.1mg/L = 0.7meq/L; Ca
++
= 7.21mg/L = 0.36meq/L; Mg
++
= 3.09mg/L = 0.254 meq/L
FM = (0.36 + 0.254)/0.7
There is no ADWG value for Figure of Merit Ratio.
+
There is no health related guideline value for sodium (salt). However, for aesthetic reasons (taste) sodium should not exceed 180mg/L. Concentrations above 135mg/L will lead to taste in the water becoming noticeable. As a precautionary note sodium intake should be monitored for babies and those in the community who need to monitor the intake of salt. The recommended daily intake of sodium for babies up to the age of 6 months is 120mg per day. Higher sodium intake will not make a baby sick, but is not recommended. People who are on low sodium diets, for medical reasons, should monitor their intake and may need to drink a source of low sodium water. Waters with very high sodium can cause blood pressure problems.
+
There is no ADWG value for potassium. Potassium plays a major role in cell functioning and it can help sodium’s effect on blood pressure. The recommended daily dietary intake for potassium is 5000mg.
++
There is no ADWG value for calcium. Calcium is an important element for good health and levels between 20 – 30 mg/L are desirable in drinking water. Very high levels of calcium, however, will produce scale and clog up water pipes.
++
There is no ADWG value for magnesium. Magnesium is an important element for good health and a level around 10mg/L is desirable in drinking water. Very high levels of magnesium will produce scale and clog up water pipes.
+
There is no ADWG value for hydrogen. Hydrogen ions are derived from the dissociation of water and acids.
3
⎯
There is no ADWG value for bicarbonate. Bicarbonate is one component of alkalinity and its concentration is in a balance with carbon dioxide between the pH range of 4.4 and 8.2 and in a balance with carbonate between the pH range of 8.2 and 9.6.
3
2 ⎯
There is no ADWG value for carbonate. Carbonate is one component of alkalinity and its concentration is in a balance with bicarbonate between the pH range of 8.2 and 9.6. At a pH of 9.6 and higher, there is no carbon dioxide or bicarbonate, with all alkalinity being in the carbonate form.
⎯
There is no ADWG value for hydroxide. The hydroxyl anion is derived from the dissociation of water and from alkalis.
⎯
There is no health related guideline value for chloride however for aesthetic reasons
Page: 6 of 8
Document Number: 28162T1
Approver/s: Henry OLSZOWY

Interpretation of Water Results – Standard Water Analyses
(taste) water should not exceed 250mg/L. Chloride occurs naturally in waters from minerals and salt. Some bore waters can be extremely concentrated in chloride (brines) and consequently are very corrosive.
⎯
Fluoride is essential for good oral health and serves to guard against tooth decay. The
ADWG value for fluoride in drinking water is 1.5mg/L. Fluoride occurs naturally from fluoride-containing rocks (e.g. fluorospar) and is often found in elevated concentrations in bore waters. Concentrations of fluoride >1.5 mg/L can cause dental fluorosis and concentrations > 4 mg/L can cause skeletal fluorosis. The ideal level for fluoride in drinking waters (under Queensland conditions) ranges from about 0.6mg/L to about
0.8mg/L.
3
⎯
The ADWG value for nitrate in drinking water is 50mg/L. Guideline value will protect bottle-fed infants under 3 months from methaemoglobinaemia. Adults and children over 3 months can safely drink water with up to 100mg/L nitrate.
4
2 ⎯
Sulphate occurs naturally in surface waters and underground waters. The ADWG value for sulphate is 500mg/L and the aesthetic ADWG value is 250mg/L. Sulphate levels above 500mg/L can have purgative effects (upset stomach and vomiting). Levels <400 mg/L are considered acceptable for human consumption but levels above 250mg/L will cause aesthetic problems (appearance).
Iron occurs naturally in low concentrations (<1mg/L) in most waters (surface and underground) from the slow decomposition (weathering) of rocks. Some bore waters however could contain very high levels (>100mg/L). There is no health related guideline value for iron. However, for aesthetic reasons (taste and staining) the concentration of iron in drinking water should not exceed 0.3mg/L. The most economical way of removing iron from water is by aeration (dissolved iron is oxidized and precipitates out of solution as rust Fe
2
O
3
).
Like iron, manganese also occurs naturally in surface and underground waters, usually in low concentration (<0.1mg/L). Some bore waters may have high levels of Mn (>10mg/L).
Manganese is derived from the weathering of rocks. For health reasons the concentration of manganese in drinking water should not exceed 0.5 mg/L. The aesthetic quality (taste and staining) of drinking water will deteriorate above 0.1 mg/L. Elevated levels will also cause discolouration of washing, porcelain ware etc.
Manganese can be removed from water by aeration.
Natural waters usually contain very low levels of zinc (<0.1mg/L). There is no health related guideline value for zinc. However, for aesthetic reasons (taste) the concentration of zinc in drinking water should not exceed 3mg/L. Elevated levels are usually due to corrosion of galvanised pipes/fittings and brasses.
Aluminium in water occurs in very low concentration (<0.05mg/L) and occurs as a result of weathering of clays. There is no health related guideline value for aluminium in drinking water.
However, it is recommended that the concentration should not exceed 0.2mg/L. This guideline value is based on the concentration that occurs after flocculating the water with alum (aluminium sulphate). Levels below
0.1mg/L are desirable. Water used for renal patients must have even lower levels of aluminium (<0.01mg/L).
Boron is derived from the leaching of minerals underground and on the surface. The concentration of boron in most waters is <1mg/L. Based on an acceptable range of oral intake a concentration of up to 4mg/L in drinking water would not pose a human health risk.
Copper can occur naturally in underground water supplies after passing over a zone of mineralisation rich in copper minerals. In most waters, the copper concentration is <1mg/L. Elevated levels in household water supplies can occur from the corrosion of copper plumbing parts, especially if the water is slightly acidic (e.g. rainwater) or otherwise corrosive. High concentrations (>5mg/L) will start to colour the
Page: 7 of 8
Document Number: 28162T1
Approver/s: Henry OLSZOWY

Interpretation of Water Results – Standard Water Analyses water bluish green. For health reasons the concentration of copper in drinking water should not exceed 2 mg/L. The aesthetic quality (taste and staining) of drinking water will deteriorate above 1 mg/L.
Table 2 : Abbreviations used in these notes.
Abbreviation Units
NHMRC National Health & Medical Research Council
SWA
ADWG

S/cm mg/L
Meq/L
Standard Water Analysis
Australian Drinking Water Guidelines
Micro Siemens per centimetre
Milligrams per litre
Milli-equivalents per litre
NTU Nephelometric Turbidity Unit ppm Parts per million
1 mg/L = 1 ppm; 1 HU = 1 PCU; 1 dS/cm = 1mS/cm = 1000

S/cm
For further information please contact the Environmental Health Unit – Water Quality Section on (07)
33289310 or QHFSS Inorganic Chemistry (07) 3274 9071.
Version
1
Date Author/s
25.08.2010 Greg Crisp – Wide Bay PHU
Henry Olszowy - QHFSS
Amendments
First Issue – Next review August 2012
National Health and Medical Research Council 2004 – Australian Drinking Water Guidelines.
Water Services Association of Australia 2 January 2008 - Information and Guidance Note - Assessing the
Likelihood of Aqueous Corrosion
Water Industry Association of Australia 2000 Conference Papers - Peter Gebbie - Water Stability: What
Does It Mean And How Do You Measure It.
Hydranautics RO Water Chemistry http://www.membranes.com/docs/papers/04_ro_water_chemistry.pdf
Page: 8 of 8
Document Number: 28162T1
Approver/s: Henry OLSZOWY