Water Quality Data and Parameters

« Go Back

Observations of water quality mainly refer to concentrations of dissolved constituents in the water in terms of physical (like turbidity, conductivity etc.), chemical (like sodium, potassium, cadmium etc.) and biological parameters (like algae, bacteria etc.). Data on water quality requires collection of a water sample followed by analysis (measurement) for specific water quality parameters. Some of these water quality parameters can be measured at site, the so-called field parameters. The other parameters are analysed in a laboratory. Laboratories of different levels are distinguished HP. Level I laboratories are small laboratories located at or near the sampling location. These were originally established for determination of sediment load only, but now can also be used for determination of the water quality field parameters. Higher level laboratories (levels II and II+) are usually located in major cities and provide analytical capacity to a larger region covering more sampling locations. Sixty eight (68) water quality parameters are considered to be the Standard HP Water Quality Parameters. These parameters include many trace contaminants such as heavy metals and organic pollutants which can only be analysed at Level II+ labs. The main information about these 68 parameters is already included in the CWC water quality database. Information about additional parameters can be added by a laboratory. The physical parameters, like total suspended solids, may also be measured along with gauge-discharge observations at level I laboratories. Every lab has been assigned a ID which is a unique eight-character code which identifies each laboratory. The Lab Name is unique name given for each laboratory. Both Lab ID and Lab Name are mandatory information.

Minimum and Maximum
The maximum value represents the highest values that may be expected for the parameter under natural conditions in surface waters in India. The minimum value is also used for checking the validation. The minimum value represents the lowest value that may be expected for the parameter under natural conditions in surface waters in India. This implicates that the most parameters cannot be reported as zero (0.0) and a minimum value (a non-zero) is therefore present in the database. Exceptions are all trace organic substances and the following parameters that may be reported as zero (0.0).

Upper Warning Limit and Lower Warning Limit
These limits are provided in the database to warn the user in case the values are exceeding the usual lower or upper limits. UWL and LWL can be edited by the laboratory, but must meet the criteria:UWL-Maximum and LWL-Minimum.

Limit of Detection
The lowest concentration that can be detected by a specific analytical method is indicated here. The LOD value is only used for validation purposes in case of trace metals and trace organics.

Calculated Parameters
Some of the parameters need not be entered in the form because they are automatically calculated. These parameters are called indirect parameters. Eight (indirect) parameters are calculated based on the measured results of other (direct) parameters. These are Sodium Adsorption Ratio (SAR), Percent Sodium, Residual Sodium Carbonate (RSC), Calcium Hardness, Total Hardness, Calculated Total Dissolved Solids, Phenolphthalein Alkalinity, and Total Alkalinity.

Ion balance for cations and anions
The relative imbalance between the sum of the major cations and the sum of the major anions s expressed in % and should not exceed 5-10%. The percent difference may be somewhat lower for samples with low TDS values. Na and Cl ratio-Normally, in sodium dominated waters, most of the Na is associated with Cl, and thus, the ratio between Na and Cl (in meq/L) remains within 0.8 to 1.2.

EC and TDS ratio
for fresh water conductivity (EC, in µmhos/cm) and Total Dissolved Solids (in mg/L) usually obey the following relationship: EC = TDS*a, Where a ranges from 0.55 to 0.9. The constant a is usually high for chloride rich waters and low for sulphate rich waters.

TDS-calculated and TDS-measured
The measured TDS concentration should be higher than the calculated one because the significant contributor may not be included in the calculation.

COD and BOD ratio
Values measured for COD should always be higher than BOD values.SWDES checks if the ratio COD/BOD >1 and indicates if the values do not meet this criteria.

Carbonate and pH relation

At pH values below 8.3 the CO3 ^2- (phenolphthalein alkalinity) alkalinity should be zero.

Certain parameters of water quality and their categorization are given in Table: 1.

Table:2 Water Quality Parameters and Analysis method: