Q. Is water harvesting techniques similar in urban and rural areas?
A. Water harvesting means the same in rural and urban areas. The only difference is in the scale of water harvesting. In rural areas, water harvesting is taken up along with soil conservation activities through a watershed management programme. On the other hand, in urban areas rooftop water harvesting is preferred due to lack of space.

Q. What are the advantages of water harvesting?
A.
In areas where there is inadequate groundwater availability or surface resources are either lacking or insufficient, rainwater harvesting can supplement the existing water supply schemes.

Reduces the load on sewer treatment plants by preventing the stormwater from entering in sewer treatment plants.

Reduces urban flooding

Recharging water into the aquifers help in improving the quality of existing groundwater through dilution and also helps in preventing the decline of water table

Q. Whether water harvesting could be done in buildings, which are already constructed?
A. Rainwater harvesting is possible in existing buildings by connecting the rooftop rainwater pipes either to a recharge or a storage structure.

Q. I live in a place where the water table is shallow and quality of uninterrupted water supply is extremely good. Under this circumstances what is the need of water harvesting in my area?
A. Shallow water table does not guarantee that the water table will remain at the same level forever. Rapid urbanisation and industrialisation has seen many a cities facing problems due to groundwater depletion. The reason being the decreased rate of groundwater recharge compared to the higher rate of extraction of the same. In Delhi for example water table has gone down by the extent of 30 m at certain locations. Hence it would be a better to utilise fully the runoff of during rainy seasons for the groundwater rather than to push us into a crisis. (According to a study conducted by Central Groundwater board (CGWB) at various locations in India, it had been found that the intake capacity of the aquifer (the rate of recharge) is high if the static water table is more than 15 m below the ground level).

Q. Can we harvest the rainwater falling on the paved and unpaved areas?
A. Whether the harvested water is used for direct usage or for recharging the groundwater, it is of utmost importance to ensure that the rainwater collected is free of any pollutants that might be added either from the atmosphere or the catchment. While polluted water directly used for consumption would have an immediate impact on health, polluted water recharged into the groundwater would cause long-term problems of aquifer pollution. Damage done to aquifers by recharging polluted water is irreversible. Hence it is advisable not to go in for groundwater recharge in those areas where control over the quality of recharged water is not possible.

In establishments like industries, it is very necessary to ensure that the catchment surfaces are free of chemical wastes, fuels, lubricants etc. Water from lawns could be harvested, provided the use of chemical fertilisers and pesticides are avoided. While sedimentation and filtration can easily remove physical and biological impurities in water, it is difficult to remove chemical impurities.

Q. Can we use the water in the stormwater drain running along the colonies/roads for recharge?
A.The stormwater drains in the colonies could be used for groundwater recharge provided bathroom water is not discharged into them and periodic cleaning of these drains are taken up. It must also be ensured that under no circumstances the sewage enters the stormwater drain. However in the case of drains running along the roads/public places, there is no control over the quality of water that is discharged into the drains and hence it is advisable not to use this water for recharging.

Q. If I use rainwater from my rooftop to recharge the groundwater, will the benefits not disperse to other water users in the neighbourhood?
A. Groundwater is not static and does not have any boundaries. Hence the recharged water cannot be localised to the area where it is recharged. Rate of groundwater flow varies widely from place to place depending on the hydrogeology, sometimes being as low as a few millimetres per day. In Delhi, for example, the vertical hydraulic conductivity of the soil formations is more than the horizontal hydraulic conductivity, which means that the rate of vertical (downward) passage of water through soil pores or rock fissures is more than the rate of horizontal flow.

Presence of recharge wells in an area can influence the wells used for extracting water in it’s close proximity. It will also to some extent, benefit groundwater users in the neighbourhood. The benefits could be more equitably distributed if water harvesting is taken up at a community-level with each user playing an active role in recharging the groundwater.

Q. What are the costs of constructing water harvesting facilities?
A.Water harvesting techniques are site specific and hence the cost of installation varies from place to place. Moreover the cost depends on the amount of water to be harvested. Typically, installing a water harvesting system in a building would cost between Rs 3,000 to 30,000 for buildings of total plot area of about 300 sq. m. Some basic rates of construction activities have been given on table given below which may be helpful in calculating the total cost of a structure.

(If the rooftop rainwater outlets are widely scattered around the building, the amount of pipe required in connecting these outlets to the recharge or storage structure would be more. Thereby increasing the cost.)

                         Table: Unit cost of construction activities.