Grey Water Use can Reduce Huge Water Crisis in Dhaka Megacity

Water is an indispensable natural resource without which existence of life is impossible. On an average a minimum quantity of 200 litres of water is used by each person a day. Plants absorb millions of liters of water everyday and about 95% transpirate to the atmosphere by using 5% only. A single tomato plant transpirates 150 liters of water in its lifetime, i.e. 3 to 4 months period only. Although water is a Non-depletable resource like cosmic or solar energy but fresh water may be regarded as depletable resource because of acute shortage of water has arisen in many areas of the world. This water shortage is either local or due to pollution or misuse. Although the total resources of water of the earth are inexhaustible still a great scarcity of fresh water exists in Bangladesh, where average rainfall is as high as 2000 mm/year and 143,000 m³/ sec of water flows by the rivers.
Shortage of water in different areas is becoming a serious problem although Bangladesh is one of the richest countries in the world in fresh water resources. This shortage is not for the increasing demand of water for irrigation, domestic and industrial uses but pollution of water and depletion underground water tables and destruction of freshwater reservoirs like Haors, Bheels, Jheels, Dighies and Ponds etc. and of course withdrawal of water from the upstream.
Due to withdrawal of water, and disturbance of natural flow, most of the rivers are drying up in the dry season and salinity is increasing in the downstream. The overall situation of water resources of Bangladesh is very deplorable. This crisis is not only affecting the city lives but the whole agriculture is in a very alarming situation.
Dhaka city with 15 million populations needs 200X15, 000,000 liters or 3,000,000,000 liters or 3,000,000 m³ of fresh water, a day. Moreover, a huge quantity of water is used in the industries everyday. To manufacture of one ton paper needs 100 m³, for one ton synthetic fibers 2500 to 5000 m³, for melting one ton steel 200 m³ and for processing one ton raw natural rubber 20 m³ fresh water is required. In Dhaka megacity more than 70% water used from the ground water. Use of surface water has been decreasing alarmingly and ground water-table is going down alarmingly. From a survey in Uttara Model Town it has been found that, none is using grey water (used water) even for agriculture, lawn, roof-top or kitchen gardening. Thus it proves that, no reuse of ground water is being done; the total 3,000,000 cubic meter water is being misused everyday and draining out to the waste water bodies which is a great loss of the natural resource as well as deterioration of the environment.
The rivers, flowing around the cities, the Turag, Balu, Buriganga and Sitalaska have been turned into open sewage canals. Industrial wastes from the dyeing and garments, leather, chemicals and medicine factories and poultry farms etc., communal or domestic garbage, faeces and many other harmful substances are being dumped to the rivers and fresh water bodies.
Therefore, it is utmost essential to take immediate measures to mitigate the rising water crisis. We have to be very careful in water uses. Domestic and industrial wastes must not be discharged into the water bodies without treatment.
The use of grey water at least for washing, gardening or agriculture can reduce huge quantity of ground water usages.

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Director, CGEC International University of Business Agriculture and Technology Bangladesh