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Chapter: Civil : Water Resources and Irrigation Engineering : Irrigation Water Requirements

Water characteristics and quality

Physical characteristics, Chemical characteristics, Biological characteristics

Water characteristics and quality:

ü        Physical  characteristics


ü        Chemical characteristics


ü        Biological characteristics




Physical  characteristics




ü      the clarity of water Transparency of natural water bodies is affected by human activity, decaying plant matter, algal blooms, suspended sediments, and plant nutrients


ü      Turbidity provides an inexpensive estimate of total suspended solids


ü      TSS concentration Turbidity has little meaning except in relatively clear waters but is useful in defining drinking-water quality in water treatment measures how deep a person can see into the water


Total Solids (TS) - the total of all solids in a water sample


Total Suspended Solids (TSS) - the amount of filterable solids in a water sample, filters are dried and weighed

Total Dissolved Solids (TDS) - Non filterable solids that pass through a filter with a pore size of 2.0 micron, after filtration the liquid is dried and residue is weighed EPA Secondary Drinking Water Recommendation is for TDS of less than 500mg/L Volatile Solids (VS) - Volatile solids are those solids lost on heating to 500 degrees C - rough approximation of the amount of organic matter present in the solid fraction of wastewater




Chemical Characteristics


Commonly measured chemical parameters are:








'Nitrates, Nitrites, & Ammonia




'Dissolved Oxygen & Biochemical Oxygen Demand




The pH of water determines the solubility of many ions and biological availability of chemical constituents such as nutrients (phosphorus, nitrogen, and carbon) an heavy metals (lead, copper, cadmium)



ü        Hard water is found in about 85% of USA.


ü        Prevents lathering/sudsing - hotter water and extra rinse cycles may be required


ü        Fabric appearance declines & life may be reduced


ü        Minerals may clog pipes & cause excessive wear on moving parts



'Distill water to remove the calcium and magnesium


'Soften the Water - Replaces calcium and magnesium ions with sodium or potassium ions


Cation exchange

Strong adsorption » » » Weak adsorption

Al+3 > Ca+2 > Mg+2 > K + = NH4+ > Na + >H +


Nitrogen   gas   (N2)   makes   up   78.1%   of   the


ü        An essential nutrient required by all plants and animals for formation of amino acids (the molecular units that make up protein) N must be "fixed" (combined) in the form of ammonia (NH3) or nitrate (NO3) to be used for growth


'N2 + 8H+ + bacteria = 2NH3 + H2

'NH3 + O2 + bacteria = NO2- + 3H+ + 2e-

'NO2- + H2O + bacteria = NO3- + 2H+ +2e-


ü        Ammonia NH3 (extremely toxic) continually changes to ammonium NH4 + (relatively harmless) and vice versa, relative concentration depends on temperature & pH At higher temperatures and pH, more N is in the ammonia form


Maximum Contaminant Level (MCL): nitrite-N : 1 mg/L nitrate-N : 10 mg/L

nitrite + nitrate (as N) : 10 mg/L


Fertilized areas; Sewage disposal; Feed lots; N cycle




ü        Secondary Drinking Water Standard EPA recommendation'total phosphate should be <0.05 mg/L (as phosphorus) in a stream where it enters a lake or reservoir


ü        total phosphate should not exceed 0.1 mg/L in streams that do not discharge directly into lakes or reservoirs



 Erosion; Fertilizer; Sewage; Feed lots; Detergents


Dissolved Oxygen


ü        Dissolved Oxygen DO mg/L 'only gas routinely measured in water samples (depends on temperature, salinity, and pressure)


ü          Analysis should be performed on site immediately after sampling


ü        Oxygen enters the water by photosynthesis of aquatic biota transfer across the air-water interface


ü        DO < 5mg/L stresses aquatic life (the lower the concentration, the greater the stress)




Biological Characteristics

Harmless bacteria ~ present in large numbers

ü        in feces and intestinal tracts of humans and


ü                    other warm-blooded animals Environmental Impact


ü          indicator of contamination with human or animal fecal material


may indicate contamination by pathogens or disease producing


ü        bacteria or viruses Criteria


ü        Swimming ~ fewer than 200 colonies/100 mL


ü          Fishing and boating ~ fewer than 1000 colonies/100 mL


ü        Domestic water supply ~ fewer than 2000 colonies/100 mL


ü        Drinking water 0 colonies/100mL


Biological Oxygen Demand


ü        Biological Oxygen Demand is a measure of oxygen used by microorganisms to decompose organic waste (add a microorganism seed to all samples seal sample dead plants, leaves, samples, from air, store in dark to prevent photosynthesis, subtract seeded control, measure decrease in DO)

ü        Nitrates & phosphates are plant


ü        nutrients so may contribute to high


ü        BOD levels When BOD levels are high, dissolved


ü        oxygen decreases ' fish and other grass clippings, manure, sewage, or food waste aquatic organisms may not survive

An index of the degree of organic pollution in water

BOD level of 1-2 ppm - very good

BOD level of 3-5 ppm - moderately clean BOD level of 6-9 ppm - somewhat polluted



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Civil : Water Resources and Irrigation Engineering : Irrigation Water Requirements : Water characteristics and quality |

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