πFluctuations in water demand:
- In India the maximum daily demand of water is generally taken as 180% of the annual average daily demand of water ( peak factor = 1.8 )
- In India the maximum hourly demand of water is generally taken as 150 per cent of the hourly demand on the day of maximum use of water ( or the maximum day for the year). [Peak Factor = 1.5]
- Average Daily per capita Demand = Quantity required in 12 months / (365 x population)
- Maximum daily demand = 1.8 x average daily demand.
- Maximum hourly demand of maximum day i.e. Peak demand = 1.5 x average hourly demand on a maximum day
= 2.7 x annual average hourly demand
π Water Quality Parameters
1.Conductivity or Electrical Conductivity (EC): is the ability of water to carry an electrical current. Pure water is a poor conductor of electricity and water shows significant conductivity when dissolved salts are present (generally, directly proportional to the amount of salts dissolved in the water). It is measured using conductivity sensors, and is expressed as siemens/meter (S/m).
2.Colour: It is an important from the standpoint of aesthetics. Colour in water is often caused by organic substances such as algae or humic compounds. The colour could be Apparent (caused by suspended matter) or True (caused by dissolved or colloidal solids).
For measurement purpose, the colour produced by 1 mg/L of platinum (as K2PtCl6) and 0.5 mg/L of
cobalt (as CoCl2•6H2O) is taken as the standard one unit of colour, and a sequential dilution method
may be followed to determine the colour in standard colour units. Spectrophotometric determination of colour in the form of absorbance at select wavelength is also getting popular.
2. Odour: in water is objectionable. Pure water is odourless, but water may acquire odour when some
substances are dissolved. Decayed organic substances give fouling smell while inorganic substances
give earthy smell.
- Odour is measured through Threshold Odour Test, where dilution factor is determined to make the water odourless.
- Threshold Odour Numbers (TON) can be computed as:
= (Volume of Sample + Volume of Pure Water needed to remove any odour)/Volume of Sample
3. Turbidity: is an optical property, describing the clarity, or haziness of the water caused by the presence of very fine suspended or colloidal particles (typically not filterable by routine methods). Turbid waters are unacceptable to consumers. Turbidity may also affect the treatability of waters.
- Turbidity is measured through passing a beam of light through the sample, and recording its scattering. The quantity of light scattered is dependent upon the concentration and size distribution of the particles.
a) In turbidimetry, the intensity of light transmitted is measured.
b) In nephelometry the intensity of the light scattered at 900 is measured.
4. Hardness: in water is caused by the presence of Ca2+ and Mg2+ ions as Hydrogencarbonate ‐ Ca(HCO3)2, Mg(HCO3)2 ; Sulphates‐ CaSO4, MgSO4 ; Chloride ‐ CaCl2, MgCl2 etc. Bicarbonates of Ca and Mg leads to Temporary Hardness, while sulphates/chlorides/nitrates of Ca and Mg leads to Permanent Hardness.
- Hardness is most commonly measured by titration with an EDTA solution, however test strips or
instruments separately measuring Ca and Mg are also being used. Hardness can also be collocated
using ion balance where equivalence of Ca2+ and Mg2+ are estimated after converting each ion as mg/L of CaCO3.
5. Solids : refers to the mass of solids present in the water. The Total Solids (TS) mass present in the water could be in suspended or dissolved state, and could be volatile or fixed by nature. Based on these different measures of solids are estimated. The measurements are done using gravimetric analysis.
- Inorganic salts in water often remains in dissolved state and are non‐volatile even at high temperatures, therefore contributes to Fixed Dissolved Solids (FDS). While, Fixed Suspended Solids (FSS) are inorganic particles suspended in the liquid; such as undissolved salt crystals and silt particles.
- Organic compounds are often volatile at high temperature. The dissolved organics e.g. sugars, fatty acids etc. constitutes Volatile Dissolved Solids (VDS), while suspended organics and microorganisms constitute Volatile Suspended Solids (VSS).
- Sum of FDS and VDS forms Total Dissolved Solids (TDS), while sum of VSS and FSS is called Total Suspended Solids (TSS).
6. Most Probable Number (MPN) : is most commonly applied parameter for microbial quality testing of water. Fecal coliforms act as an indicator for fecal contamination of water.
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