Present Water Supply Demand and Future need

Present Water Supply Demand and Future need

As per the norms stipulated in the code of basic requirements of water supply, drainage and sanction as well as national building code (ISI 172), a minimum of 135 litres per capita per day has to be provided to all the residents with full flushing system of toilets. Apart from this, the institutional demands also have to be considered. A large number of central and state institutions including universities, hospitals, hotels, railway stations, restaurants, airports, bus stations, theatres, parks etc., have to be supplied with water both for drinking and sanitation purpose. Furthermore a large number of industries have also to be taken care of.

A study conducted by CGWB in Hyderabad and Visakhapatnam on 'Source and Demand' of water suggested that there exists deficit of water supply. In Hyderabad it is to the tune of about 380 MLD and Visakhapatnam about 12 MGD. Tapping and using the ground water can bridge the deficit.

This deficit between supply and demand is bound to increase in the future with an increase in population. According to CGWB report, the demand for water in Hyderabad city in 2021 will be 2000 MLD and in Visakhapatnam it will be 60 MGD in 2011. Most of the deficit has to be met by rational use of ground water.

The evaluation of ground water quality is as important as quantity, since the usability of water is determined by its chemical characteristics. The quality of ground water depends upon the nature of rock formation, physiography, soils, environment, recharge and discharge conditions in the area. Mineral water reaction is also an important criterion. Artificial pollution sources like sewerage, organic and other waste dumps, and chemical dumps too cause considerable ground water pollution particularly in the urban areas.

The following are the major chemical components of ground water:

Na+, K+, Mg2+, Ca2+, HCO3, SO4, Cl-.

Electrical Conductivity

The EC of water is defined as "the reciprocal of the resistance in ohms and it measures the ability of water to conduct electrical current at a specified temperature, expressed in micro siemens at 25O Celsius. It indicates the amount of mineralisation of ground water. ISI prescribed 500mg/1 of total dissolved solids (TDS) as a desirable limit and 2000mg/1 as maximum permissible limit in the absence of alternate source of water. These limits approximately correspond to 750 and 3000 micro siemens/cm at 25 degrees celsius, beyond this limit the palatability of water decreases and may cause gastro-intestinal irritation.

Total Hardness:- TH is the equivalent concentration of calcium carbonate. It is a measure of the capacity of the water to react with soap. As per ISI standards the desirable limit is 300mg/ltr, beyond which encrustation of structures may result. The maximum permissible limit is 600mg/ltr. Classification of water in terms of hardness is

Concentration (mg/ltr)	Degree
0-75	Soft
75-100	Moderately soft
150-300	Hard
300	Very Hard

Calcium: For drinking purposes, ISI desirable limit of calcium is 75mg/ltr and the maximum permissible limit is 200mg/ltr. Excessive concentration of Ca and Mg in drinking water will lead to formation of concretions in body and may cause gastro-intestinal problems and stone formations.

Magnesium: Magnesium is essential for plant and animal nutrition. It is generally released during the process of weathering of minerals like amphiboles, pyroxenes, biotite mica, dolomite, olivine etc. As per ISI Standards, the desirable limit for drinking is 30mg/ltr and maximum permissible limit is 100mg/ltr.

Sodium: Sodium is most abundant alkaline metal. It is more in igneous rocks and less in sediments.

Potassium: An essential element for both plants and animals, principal sources of potassium are orthoclase, microline, biotrite, lencite etc. Potassium content is less than sodium in water.

Chloride:- Chlorine gets readily dissolved in water. Abnormal concentration of chlorine in ground water is due to pollution by sewerage. As per ISI Standards the desirable limit for drinking water is 250mg/ltr and maximum permissible limit in the absence of alternate source is 1000mg/ltr.

Nitrate: Nitrogen is a major constituent of atmosphere. Soil bacteria convert it into nitrite and nitrate. Nitrate is a minor constituent of rocks. Part of the nitrate is fixed by the plants before the rain water percolates below the root zone. Natural ground water contains less than 5mg/ltr of nitrates. But the polluted waters contain high concentrations of nitrate.

As per ISI norms, the nitrate concentration upto 45mg/ltr is desirable limit for drinking. Beyond this limit, Methaemoglobinaemia takes place, mostly in babies. The maximum permissible limit is 100mg/ltr.

Sulphate: As the ground water passes through the minerals, concentration of sulphate is possible. Recommended desirable limit is 200mg/ltr and the maximum limit for drinking purposes is 400mg/ltr.

Fluoride: The concentration of fluoride in ground water is due to solubility of fluoride bearing minerals like fluorite, cryolite, topaz, mica etc. As per ISI Standards 1.0mg/ltr is the desirable limit whereas 1.2mg/ltr is the permissible limit in the absence of an alternate source. Above 1.5mg/ltr it causes fluorosis disease.